Cation exchange membrane, electrolysis vessel using the same and method for producing cation exchange membrane

ABSTRACT

Provided is a cation exchange membrane having excellent mechanical strength against folding and the like and capable of delivering stable electrolytic performance for a long time, an electrolysis vessel using the cation exchange membrane and a method for producing the cation exchange membrane. A cation exchange membrane  1  at least includes: a membrane body containing a fluorine-based polymer having an ion-exchange group; and two or more reinforcing core materials arranged approximately in parallel within the membrane body. The membrane body is provided with two or more elution holes  12  formed between the reinforcing core materials  10  adjacent to each other. In addition, assuming that a distance between the reinforcing core materials  10  adjacent to each other is represented by a, a distance between the reinforcing core materials  10  and the elution holes  12  adjacent to each other is represented by b, a distance between the elution holes  12  adjacent to each other is represented by c, and the number of the elution holes  12  formed between the reinforcing core materials  10  adjacent to each other is represented by n, then a, b, c, and n satisfying the relationship represented by the following expression (1) or expression (2) are at least present.
 
 b&gt;a /( n +1)  (1)
 
 c&gt;a /( n +1)  (2)

The present application is a divisional of U.S. application Ser. No.13/503,975, which is a National stage of International PatentApplication No. PCT/JP2010/068855 filed Oct. 25, 2010, which claimspriority to Japanese Application No. 2009-245869 filed Oct. 26, 2009.The disclosures of U.S. application Ser. No. 13/503,975 andInternational Patent Application No. PCT/JP2010/068855 are incorporatedby reference herein in their entireties.

TECHNICAL FIELD

The present invention relates to a cation exchange membrane, anelectrolysis vessel using the same and a method for producing the cationexchange membrane.

BACKGROUND ART

A fluorine-containing ion exchange membrane is excellent in e.g., heatresistance and chemical resistance. Therefore, the fluorine-containingion exchange membrane has been used not only as a cation exchangemembrane for alkali chloride electrolysis for producing chlorine and analkali but also a diaphragm for generating ozone, a fuel cell, widevariety of diaphragms for electrolysis such as water electrolysis andhydrochloric acid electrolysis. Of them, the membrane for use in alkalichloride electrolysis is demanded to, e.g., increase current efficiencyin view of productivity, reduce electrolysis voltage in view of economicefficiency and reduce the concentration of sodium chloride in causticsoda in view of quality of a product.

Of these demands, in order to increase current efficiency, an ionexchange membrane formed of at least two layers, i.e., a carboxylic acidlayer using a carboxylic acid group having high anion eliminationproperty as an ion-exchange group and a sulfonic acid layer using a lowresistant sulfonic acid group as an ion-exchange group, is generallyused. Since these ion exchange membranes are brought into direct contactwith chlorine and caustic soda of from 80 to 90° C. during anelectrolysis operation, a fluorine-based polymer having extremely highchemical resistance is used as a material for the ion exchange membrane.However, the ion exchange membrane formed of such a fluorine-basedpolymer alone does not have sufficient mechanical strength. Therefore,the membrane is reinforced, for example, by embedding a woven fabriccontained of polytetrafluoroethylene (PTFE) in the membrane, as areinforcing core material.

For example, Patent Document 1 proposes a fluorine-based cation exchangemembrane for electrolysis composed of a first layer, which is formed ofa fluorine-based polymer film having a cation-exchange group andreinforced with the woven fabric, and a second layer, which is formed ofa fluorine based polymer having a carboxylic acid group and positionedon the cathode side, in which ≧½ of the thickness of a porous basematerial is projected from the first layer toward the anode side, theprojecting part of the porous base material is covered with a coatinglayer of the fluorine-based polymer having the cation-exchange group soas to integrate into the first layer and to form the convexo-concavesalong with the surface shape of the porous base material on the anodeside surface.

-   Patent Document 1: Japanese Patent Application Laid-Open No.    4-308096

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, the reinforcing core material acts as a blocking material for acation such as alkali ion when flowing from the anode side to thecathode side within the membrane thereby preventing the cation fromflowing from the anode side to the cathode side smoothly. To solve thisphenomenon, a hole (hereinafter, referred to as an “elution hole”) isformed in the cation exchange membrane for ensuring a flow channel fore.g., a cation and an electrolyte and used as an electrolyte flowchannel. In this manner, the electrical resistance of the cationexchange membrane is expected to be reduced. However, the strength ofthe cation exchange membrane is reduced by the presence of the elutionhole. Particularly, in the case where the cation exchange membrane ismounted to an electrolysis vessel and the case where the cation exchangemembrane is carried, the cation exchange membrane folds or bends therebygenerating a problem of likely developing a pinhole from the elutionhole. In the cation exchange membrane disclosed in Patent Document 1,the reinforcing core material projects from the cation exchangemembrane. Therefore, when the cation exchange membrane rubs against anelectrode or the like due to e.g., vibration within an electrolysisvessel, a resin covering the reinforcing core material is peeled off andthe reinforcing core material is exposed therefrom, causing a problem oflosing the function as a reinforcing member.

In addition, when the cation exchange membrane is mounted to theelectrolysis vessel to perform electrolysis, reduction in voltage(electrolysis voltage) required for electrolysis is demanded. To realizethis, the cation exchange membrane has desirably low resistance.Furthermore, the cation exchange membrane capable of delivering stableelectrolytic performance for a long time is desired.

The present invention has been made in view of the aforementionedcircumstances. It is a main object of the present invention is toprovide a cation exchange membrane having excellent mechanical strengthagainst folding or the like, delivering stable electrolytic performancefor a long time, an electrolysis vessel using the cation exchangemembrane and a method for producing the cation exchange membrane.

Means for Solving the Problems

The present inventors have made intensive studies with the view forattaining the aforementioned objects. As a result, they found thataforementioned objects can be attained by a cation exchange membranehaving at least a membrane body containing a fluorine-based polymerhaving an ion-exchange group and two or more reinforcing core materialsarranged approximately in parallel within the membrane body, in whichthe membrane body has two or more elution holes formed between thereinforcing core materials adjacent to each other, and assuming that adistance between the reinforcing core materials adjacent to each otheris represented by a; a distance between the reinforcing core materialsand the elution holes adjacent to each other is represented by b; adistance between the elution holes adjacent to each other is representedby c; and the number of the elution holes formed between the reinforcingcore materials adjacent to each other is represented by n, then a, b, c,and n satisfying a specific relational expression are present. Based onthis, the present invention has been accomplished.

More specifically, the present invention is as follows.

[1] A cation exchange membrane at least comprising:

a membrane body containing a fluorine-based polymer having anion-exchange group; and

two or more reinforcing core materials arranged approximately inparallel within the membrane body,

wherein the membrane body is provided with two or more elution holesformed between the reinforcing core materials adjacent to each other,and

assuming that a distance between the reinforcing core materials adjacentto each other is represented by a, a distance between the reinforcingcore materials and the elution holes adjacent to each other isrepresented by b, a distance between the elution holes adjacent to eachother is represented by c, and the number of the elution holes formedbetween the reinforcing core materials adjacent to each other isrepresented by n, then a, b, c, and n satisfying the relationshiprepresented by the following expression (1) or expression (2) are atleast present.b>a/(n+1)  (1)c>a/(n+1)  (2)[2] The cation exchange membrane according to [1], wherein a, c, and nfurther satisfy the relationship represented by the following expression(3).0.2a/(n+1)≦c≦0.9a/(n+1)  (3)[3] The cation exchange membrane according to [1] or [2], wherein a, b,and n further satisfy the relationship represented by the followingexpression (4).a/(n+1)<b≦1.8a/(n+1)  (4)[4] The cation exchange membrane according to [1] or [3], wherein a, c,and n further satisfy the relationship represented by the followingexpression (5).1.1a/(n+1)≦c≦0.8a  (5)[5] The cation exchange membrane according to any one of [1] to [4],wherein

a first interval between the reinforcing core materials in which a, b,c, and n satisfy the relationship represented by the expression (1), and

a second interval between the reinforcing core materials in which a, b,c, and n satisfy the relationship represented by the expression (2) arealternately present.

[6] The cation exchange membrane according to [5], wherein

in the first interval between the reinforcing core materials, a, b, c,and n further satisfy the relationships represented by the followingexpression (3) and the following expression (4), and

in the second interval between the reinforcing core materials, a, b, c,and n further satisfy the relationship represented by the followingexpression (5).0.2a/(n+1)≦c≦0.9a/(n+1)  (3)a/(n+1)<b≦1.8a/(n+1)  (4)1.1a/(n+1)≦c≦0.8a  (5)[7] The cation exchange membrane according to [5] or [6], wherein thefirst interval between the reinforcing core materials satisfying therelationship represented by the following expression (6) and the secondinterval between the reinforcing core materials satisfying therelationship represented by the following expression (7) are alternatelypresent.n=2,b>a/3  (6)n=2,c>a/3  (7)[8] The cation exchange membrane according to any one of [5] to [7],wherein the first interval between the reinforcing core materialssatisfying the relationship represented by the following expression (8)and the second interval between the reinforcing core materialssatisfying the relationship represented by the following expression (9)are alternately present.n=2,0.2a/3≦c≦0.9a/3,a/3<b≦1.8a/3  (8)n=2,1.1a/3≦c≦0.8  (9)[9] The cation exchange membrane according to [1], wherein a, b, c, andn satisfying the relationship represented by the above expression (1) orthe above expression (2) are at least present in a MD direction and in aTD direction of the cation exchange membrane.[10] The cation exchange membrane according to [6], wherein the firstinterval between the reinforcing core materials satisfying therelationships represented by the expression (3) and the expression (4)or the second interval between the reinforcing core materials satisfyingthe relationship represented by the expression (5) is present in the MDdirection and in the TD direction of the cation exchange membrane.[11] A method for producing the cation exchange membrane, comprising thesteps of:

weaving two or more reinforcing core materials, a sacrifice yarn solublein an acid or an alkali, and a dummy yarn soluble in a predeterminedsolvent in which the reinforcing core materials and the sacrifice yarnare insoluble, to obtain a reinforcing material having the sacrificeyarn and the dummy yarn arranged between the reinforcing core materialsadjacent to each other;

soaking the reinforcing material in the predetermined solvent to removethe dummy yarn from the reinforcing material;

stacking the reinforcing material from which the dummy yarn is removedand a fluorine-based polymer having an ion-exchange group or anion-exchange group precursor which can be converted into theion-exchange group by hydrolysis, to form a membrane body having thereinforcing material; and

soaking the sacrifice yarn in an acid or an alkali to remove thesacrifice yarn from the membrane body, thereby forming an elution holein the membrane body.

[12] An electrolysis vessel at least comprising: an anode; a cathode;and the cation exchange membrane according to any one of [1] to [10]arranged between the anode and the cathode.

Advantageous Effects of the Invention

According to the present invention, it is possible to provide the cationexchange membrane having excellent mechanical strength against folding,etc. and capable of delivering stable electrolytic performance for along time, and the method for producing the cation exchange membrane.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a sectional side view of the first embodiment of the cationexchange membrane according to the present embodiment.

FIG. 2 shows a conceptual diagram of the first embodiment of the cationexchange membrane according to the present embodiment.

FIG. 3 shows a conceptual diagram of the second embodiment of the cationexchange membrane according to the present embodiment.

FIG. 4 shows a conceptual diagram of the third embodiment of the cationexchange membrane according to the present embodiment.

FIG. 5 shows a conceptual diagram of the fourth embodiment of the cationexchange membrane according to the present embodiment.

FIG. 6 shows a conceptual diagram of the fifth embodiment of the cationexchange membrane according to the present embodiment.

FIG. 7 shows a conceptual diagram for illustrating an example of theproducing method according to the present embodiment.

FIG. 8 shows a conceptual diagram of a cation exchange membrane preparedin Examples and Comparative Examples.

FIG. 9 shows a conceptual diagram of another cation exchange membraneprepared in Examples and Comparative Examples.

FIG. 10 shows a conceptual diagram of the electrolysis vessel accordingto the present embodiment.

MODES FOR CARRYING OUT THE INVENTION

Hereinafter, the best mode for carrying out the present invention(hereinafter referred to as “the present embodiment”) will be morespecifically described. Note that, the present invention is not limitedto the present embodiments below and can be modified in various wayswithin the scope thereof and carried out. Note that, in the drawings,the positional relationship such as right—left or up—down, is based onthe positional relationship shown in the drawings unless otherwisespecified. Furthermore, the dimensional ratio of a drawing is notlimited to that shown in the drawing.

<Cation Exchange Membrane>

FIG. 1 is a sectional side view of a first embodiment of the cationexchange membrane according to the present embodiment. FIG. 2 is aconceptual diagram of a first embodiment of the cation exchange membraneaccording to the present embodiment. A cation exchange membrane 1 is acation exchange membrane at least comprising: a membrane body 14containing a fluorine-based polymer having an ion-exchange group; andtwo or more reinforcing core materials 10 arranged approximately inparallel within the membrane body 14. The membrane body 14 is providedwith two or more elution holes 12 formed between the reinforcing corematerials 10 adjacent to each other. In addition, assuming that adistance between the reinforcing core materials 10 adjacent to eachother is represented by a, a distance between the reinforcing corematerials 10 and the elution holes 12 adjacent to each other isrepresented by b, a distance between the elution holes 12 adjacent toeach other is represented by c, and the number of the elution holes 12formed between the reinforcing core materials 10 adjacent to each otheris represented by n, then a, b, c, and n satisfying the relationshiprepresented by the following expression (1) or expression (2) are atleast present.b>a/(n+1)  (1)c>a/(n+1)  (2)

The membrane body 14 has a function of selectively passing a cation andcontains a fluorine-based polymer. The membrane body 14 preferably hasat least a sulfonic acid layer 142 having a sulfonic acid group as theion-exchange group and a carboxylic acid layer 144 having a carboxylicacid group as the ion-exchange group. Generally, the cation exchangemembrane 1 is used such that the sulfonic acid layer 142 is positionedon the anode side (α) of the electrolysis vessel and the carboxylic acidlayer 144 is positioned on the cathode side (β) of the electrolysisvessel. The sulfonic acid layer 142 is formed of a lowelectrical-resistance material and preferably has a large film thicknessin view of membrane strength. The carboxylic acid layer 144 preferablyhas a high anion elimination property even if the film thickness is low.By containing the carboxylic acid layer 144 as mentioned above,selective permeability of a cation such as a sodium ion can be furtherimproved. The membrane body 14 is satisfactory as long as it has afunction of selectively passing the cation and contains a fluorine-basedpolymer, and the structure thereof is not necessarily limited to theaforementioned structure. The term “anion elimination property” usedherein refers to a property of preventing invasion or permeation of ananion into the cation exchange membrane.

The fluorine-based polymer used in the membrane body 14 may include afluorine-based polymer having an ion-exchange group or an ion-exchangegroup precursor which can be converted into an ion-exchange group byhydrolysis, formed of a fluorinated hydrocarbon as a main chain with afunctional group capable of converting into an ion-exchange group bye.g., hydrolysis as a pendant side chain and to which melt processing isapplicable. An example of the method for producing such thefluorine-based polymer will be described below.

The fluorine-based polymer can be produced by, for example,copolymerization of at least one monomer selected from the followingfirst group and at least one monomer selected from the following secondgroup and/or the following third group, or alternatively produced byhomo-polymerization of one monomer selected from any one of thefollowing first group, second group and third group.

The first group monomer may include, for example, a vinyl fluoridecompound. Examples of the vinyl fluoride compound may include vinylfluoride, tetrafluoroethylene, hexafluoropropylene, vinylidene fluoride,trifluoroethylene, chlorotrifluoroethylene andperfluoro(alkylvinylether). Particularly, in the case where the cationexchange membrane 1 according to the present embodiment is used as amembrane for alkali electrolysis, a perfluoro monomer is preferably usedas the vinyl fluoride compound. For example, a perfluoro monomerselected from the group consisting of tetrafluoroethylene,hexafluoropropylene and perfluoro(alkylvinylether) is preferable.

The second group monomer may include, for example, a vinyl compoundhaving a functional group capable of converting into a carboxylic acidgroup (carboxylic acid type ion-exchange group). The vinyl compoundhaving a functional group capable of converting into a carboxylic acidgroup (carboxylic acid type ion-exchange group) may include, forexample, a monomer represented by CF₂=CF(OCF₂CYF)_(s)—O(CZF)_(t)—COOR(wherein s represents an integer of 0 to 2, t represents an integer of 1to 12, Y and Z each independently represent F or CF₃ and R represents alower alkyl group) and the like.

Of these, a compound represented by CF₂=CF(OCF₂CYF)_(n)—O(CF₂)_(m)—COORis preferable, where n represents an integer of 0 to 2, m represents aninteger of 1 to 4, Y represents F or CF₃ and R represents CH₃, C₂H₅ orC₃H₇. Particularly, when the cation exchange membrane according to thepresent embodiment is used as a cation exchange membrane for alkalielectrolysis, at least a perfluoro compound is preferably used as amonomer. However, since the alkyl group (see the aforementioned R) ofthe ester group is removed from the polymer at the time of hydrolysis,the alkyl group (R) may not be a perfluoroalkyl group where all hydrogenatoms are substituted with fluorine atoms. Of these, for example, themonomers shown below are more preferable;CF₂=CFOCF₂CF(CF₃)OCF₂COOCH₃,CF₂=CFOCF₂CF(CF₃)O(CF₂)₂COOCH₃,CF₂=CF[OCF₂CF(CF₃)]₂O(CF₂)₂COOCH₃,CF₂=CFOCF₂CF(CF₃)O(CF₃)₃COOCH₃,CF₂=CFO(CF₂)₂COOCH₃,CF₂=CFO(CF₂)₃COOCH₃.

The third group monomer may include, for example, a vinyl compoundhaving a functional group capable of converting into a sulfonic acidgroup (sulfone type ion-exchange group). As the vinyl compound having afunctional group capable of converting into a sulfonic acid group(sulfone type ion-exchange group), for example, a monomer represented byCF₂=CFO—X—CF₂—SO₂F is preferable (wherein X represents a perfluorogroup). Specific examples thereof may include the monomers shown below:CF₂=CFOCF₂CF₂SO₂F,CF₂=CFOCF₂CF(CF₃)OCF₂CF₂SO₂F,CF₂=CFOCF₂CF(CF₃)OCF₂CF₂CF₂SO₂F,CF₂=CF(CF₂)₂SO₂F,CF₂=CFO[CF₂CF(CF₃)O]₂CF₂CF₂SO₂F,CF₂=CFOCF₂CF(CF₂OCF₃)OCF₂CF₂SO₂F.

Of these, CF₂=CFOCF₂CF(CF₃)OCF₂CF₂CF₂SO₂F, andCF₂=CFOCF₂CF(CF₃)OCF₂CF₂SO₂F are more preferable.

From these monomers, copolymers can be produced by a polymerizationmethod developed for homo-polymerization and copolymerization ofethylene fluoride, particularly, a general polymerization method usedfor tetrafluoroethylene. For example, in a non-aqueous method, apolymerization reaction can be carried out using an inert solvent suchas perfluorohydrocarbon and chlorofluorocarbon in the presence of aradical polymerization initiator such as a perfluorocarbon peroxide andan azo compound under the conditions: a temperature of 0 to 200° C. anda pressure of 0.1 to 20 MPa.

In the above-mentioned copolymerization, the kind of combination of theabove-mentioned monomers and the ratio thereof are not particularlylimited, and selected and determined depending upon the type and amountof functional group that is desired to be added to the fluorine-basedpolymer to be obtained. For example, in order to obtain a fluorine-basedpolymer containing only a carboxylate functional group, at least onekind of monomer may be selected each from the aforementioned first groupand second group and copolymerized. Furthermore, in order to obtain apolymer containing only a sulfonyl fluoride functional group, at leastone kind of monomer may be selected each from the aforementioned firstgroup and third group and copolymerized. Moreover, in order to obtain afluorine-based polymer having a carboxylate functional group and asulfonyl fluoride functional group, at least one kind of monomer may beselected each from the aforementioned first group, second group andthird group and copolymerized. In this case, a desired fluorine-basedpolymer may be obtainable also by separately polymerizing a copolymerformed of monomers selected from the aforementioned first group andsecond group and a copolymer formed of monomers selected from theaforementioned first group and third group and thereafter mixing them.Furthermore, the mixing ratio of the monomers is not particularlylimited; however, in order to increase the amount of functional groupper unit polymer, the ratio of monomers selected from the aforementionedsecond group and third group may be increased.

The total ion exchange capacity of a fluorine containing copolymer isnot particularly limited; however, it is preferably from 0.5 to 2.0 mgequivalent/g in terms of a dry resin and more preferably from 0.6 to 1.5mg equivalent/g in terms of a dry resin. The total ion exchange capacityused herein refers to an equivalent of an exchange group per unit weightof a dry resin and can be determined by neutralization titration, etc.

The cation exchange membrane 1 of the present embodiment preferablyfurther has coating layers 146, 148, if necessary, in view of preventingdeposition of gas on the cathode-side surface and the anode-sidesurface. The material for constituting the coating layers 146, 148 isnot particularly limited; however, in view of preventing deposition of agas, an inorganic substance is preferably included. Examples of theinorganic substance may include zirconium oxide and titanium oxide. Amethod for forming the coating layers 146, 148, is not particularlylimited and a method known in the art can be used. For example, a methodof coating a liquid having inorganic oxide fine particles dispersed in abinder polymer solution by a spray, etc., can be mentioned.

The cation exchange membrane 1 has two or more reinforcing corematerials 10 arranged approximately in parallel within the membrane body14. The reinforcing core material 10 refers to a member for improvingmechanical strength of the cation exchange membrane 1 and dimensionalstability thereof. The dimensional stability as used herein refers to aproperty of suppressing the expansion and contraction of the cationexchange membrane within a desired range. The cation exchange membranehaving excellent dimensional stability does not expand and contract morethan necessary by e.g., hydrolysis and electrolysis and has stabledimensions for a long time. The member for constituting the reinforcingcore material 10 may be, but not particularly limited to, for example, areinforcing core material formed from a reinforcing yarn. Thereinforcing yarn used herein is a member for constituting thereinforcing core material and refers to a yarn capable of impartingdesired mechanical strength to the cation exchange membrane and beingstably present in the cation exchange membrane.

The form of the reinforcing core material 10 is not particularlylimited; however, for example, a woven fabric, a nonwoven fabric and aknitted fabric using the aforementioned reinforcing yarn may be used. Ofthese, in view of convenience in production, a woven fabric ispreferable. As a weave of the woven fabric, a plain weave is preferable.The thickness of the woven fabric is not particularly limited; however,it is preferably from 30 to 250 μm and more preferably from 30 to 150μm. Furthermore, the weave density (the number of woven fibers per unitlength) of the reinforcing yarn is not particularly limited; however, itis preferably from 5 to 50 yarns/inch.

The opening ratio of the reinforcing core material 10 is notparticularly limited; however, it is preferably 30% or more and 90% orless. The opening ratio is preferably 30% or more in view of theelectrochemical properties of the cation exchange membrane andpreferably 90% or less in view of the mechanical strength of themembrane. More preferably, the opening ratio is 50% or more and furtherpreferably 60% or more.

The opening ratio herein refers to a ratio of the (B) sum of areasthrough which a substance such as an ion can pass relative to the (A)sum of the surface areas of the cation exchange membrane and representedby (B)/(A). The (B) represents the sum of areas through which a cationand an electrolyte, etc. can pass without being interrupted by e.g., thereinforcing core material and the reinforcing yarn, etc. contained inthe cation exchange membrane. A method for determining the opening ratiowill be more specifically described. A surface image of the cationexchange membrane (cation exchange membrane before coating) is shot. Theareas of the regions where no reinforcing core material is present aresum up to obtain the (B). Subsequently, from the area of the surfaceimage of the cation exchange membrane, the (A) is obtained. The (B) isdivided by the (A) to obtain the opening ratio.

The material for the reinforcing yarn constituting the reinforcing corematerial 10 is not particularly limited; however, it is preferably amaterial having resistance to an acid and an alkali, etc. Particularly,a material containing a fluorine-based polymer is more preferable inview of maintaining heat resistance and chemical resistance for a longtime. Examples of the fluorine-based polymer referred to herein, mayinclude a polytetrafluoroethylene (PTFE), atetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA), aethylene-tetrafluoroethylene copolymer (ETFE), atetrafluoroethylene-hexafluoropropylene copolymer, atrifluorochlorethylene-ethylene copolymer and a polyvinylidene fluoride(PVDF). Of these, polytetrafluoroethylene (PTFE) is preferable in viewof heat resistance and chemical resistance.

The diameter of the reinforcing yarn to be used in the reinforcing corematerial 10 is not particularly limited; however, it is preferably from20 to 300 deniers and more preferably from 50 to 250 deniers. Thereinforcing yarn may be a monofilament or a multi-filament. Furthermore,a yarn thereof, a slit yarn, etc. can be used.

Particularly preferable form of the reinforcing core material 10 is areinforcing core material containing PTFE in view of chemical resistanceand heat resistance, and a tape yarn or a highly oriented monofilamentin view of strength. Specifically, a tape yarn prepared by slicing ahighly strong porous sheet formed of PTFE into tape-form pieces or aplain-weave using a highly oriented monofilament formed of PTFE of from50 to 300 deniers with a weave density of from 10 to 50 yarns/inch ispreferable and the reinforcing core material having a thickness withinthe range of from 50 to 100 μm is more preferable. Furthermore, theopening ratio of the cation exchange membrane containing the reinforcingcore material is further preferably 60% or more.

In the membrane body 14, two or more elution holes 12 are formed. Theelution holes 12 are holes that can be used as a flow channel of acation generated in electrolysis and an electrolyte. By forming theelution holes 12, mobility of an alkali ion generated in electrolysisand an electrolyte can be ensured. The shape of the elution holes 12 isnot particularly limited. In the case where the cation exchange membraneis produced in accordance with the process described later, the elutionholes 12 of the membrane body are formed by dissolving a sacrifice yarnin an acid or an alkali, thus the shape of the elution holes 12 is sameas the shape of the sacrifice yarn.

As shown in FIG. 1, the cation exchange membrane 1 has elution holes 12a formed in the perpendicular direction to the plane of paper and anelution hole 12 b formed along the longitudinal direction in parallel tothe plane of paper. That is, the elution hole 12 b formed along thelongitudinal direction in parallel to the plane of paper is formedapproximately in perpendicular to the reinforcing core material 10. Theelution hole 12 b is preferably formed such that the elution hole 12 balternately passes through the anode side (side near the sulfonic acidlayer 142) and the cathode side (side near the carboxylic acid layer144) of the reinforcing core material 10. Owing to such a structure, inthe portion where the elution hole 12 b is formed on the cathode side ofthe reinforcing core material 10, a cation (for example, sodium ion)transported through the electrolyte charged in the elution hole can flowalso on the cathode side of the reinforcing core material 10. As aresult, since a cation flow is not interrupted, the electricalresistance of the cation exchange membrane 1 can be further reduced.

Note that, in FIG. 1, the cation exchange membrane 1 has elution holes12 a formed in the perpendicular direction to the plane of paper and theelution hole 12 b formed along the longitudinal direction in parallel tothe plane of paper. The number n of the elution holes 12 formed betweenthe reinforcing core materials 10 adjacent to each other refers to thenumber of elution holes 12 arranged in the same direction. In the caseof FIG. 1, the number of elution holes 12 a formed in the perpendiculardirection to the plane of paper is specified as the number n in theperpendicular direction to the plane of paper; whereas the number ofelution holes 12 b formed along the longitudinal direction in parallelto the plane of paper is specified as the number n along thelongitudinal direction in parallel to the plane of paper.

As shown in FIG. 2, assuming that the distance between the reinforcingcore materials 10 adjacent to each other is represented by a, thedistance between the reinforcing core materials 10 and the elution holes12 adjacent to each other is represented by b, the distance between theelution holes 12 adjacent to each other is represented by c, and thenumber of the elution holes 12 formed between the reinforcing corematerials 10 adjacent to each other is represented by n, then a, b, c,and n satisfying the relationship represented by the followingexpression (1) or expression (2) are at least present.b>a/(n+1)  (1)c>a/(n+1)  (2)

In the expressions, a/(n+1) corresponds to the distance between elutionholes when they are arranged at equal intervals between the reinforcingcore materials 10. In the interval between the reinforcing corematerials 10 where a, b, c and n satisfying the relationship representedby expression (1) are present, the distance b between the reinforcingcore materials 10 and the elution holes 12 adjacent to each other islarger than the equal intervals (a/(n+1)). In this case, as the distanceb between the reinforcing core materials 10 and the elution holes 12adjacent to each other, there are two distances between the adjacentreinforcing core materials 10, that is, there are two b (morespecifically, in FIG. 2, one is present between the reinforcing corematerial 10 on the left and the elution hole 12 and the other is presentbetween the reinforcing core material 10 on the right and the elutionhole 12). In the present embodiment, it is satisfactory if at least oneof the two b satisfies the relationship of expression (1). Morepreferably, the two b present between the adjacent reinforcing corematerials 10 both satisfy the relationship of expression (1). Note that,a is the sum of all b and all c present between the reinforcing corematerials adjacent to each other, although it is apparent from thedefinition.

In the interval between the reinforcing core materials 10 where a, b, cand n satisfying the relationship represented by expression (2) arepresent, the interval c between the elution holes 12 adjacent to eachother is larger than the equal intervals (a/(n+1)). In this case, as thedistance c between the elution holes 12 adjacent to each other, thereare two or more distances c, if n=3 or more. That is, there are two ormore c. In this case, it is satisfactory if at least one of c satisfiesthe relationship of expression (2) in the present embodiment.

As is apparent from the description above, in the cation exchangemembrane 1 of the present embodiment, it is satisfactory if at least onearrangement satisfying the relationship of expression (1) or expression(2).

Furthermore, the elution holes 12 are preferably arranged at positionsapproximately symmetric to the middle of the adjacent reinforcing corematerials. At this time, the two b present between the adjacentreinforcing core materials become a approximately equal value.

If the reinforcing core materials 10 and the elution holes 12 are formedin the membrane body 14 so as to satisfy the relationship of expression(1) or expression (2), at least the mechanical strength of the cationexchange membrane 1 can be improved. By setting positional relationshipbetween the reinforcing core materials 10 and the elution holes 12 to aspecific positional relationship represented by expression (1) orexpression (2), even if the case where the cation exchange membrane 1may be fold in handing, a failure such as formation of a pinhole causedby application of excessive load to a specific site can be prevented. Asa result, the folding resistance of the cation exchange membrane 1 canbe excessively improved; excellent mechanical strength can be maintainedfor a long time; and a stable electrolytic performance can be delivered.In the present embodiment, as long as either one of expression (1) andexpression (2) is satisfied, the aforementioned effect can be obtained,however in view of mechanical strength, the relationship of expression(2) is more preferably satisfied.

In addition, electrolysis voltage can be further reduced by satisfyingexpression (1) or expression (2). Electrolysis voltage can be reduced bycontrolling the arrangement of the elution holes 12 to ensure mobilityof a cation such as an alkali ion generated in electrolysis and anelectrolyte. A method for controlling the arrangement of the elutionholes 12 may include, for example, a method of appropriately modifyingweaving conditions in a step of producing a cation exchange membrane, asdescribed later.

Furthermore, when the cation exchange membrane 1 is installed within theelectrolysis vessel, even if the cation exchange membrane 1 is rubbedagainst the electrode, etc. by e.g., vibration of the electrolysisvessel, it is possible to prevent the reinforcing core material 10 fromdamaging and sticking out through the surface of the membrane body 14.Since the reinforcing core material 10, etc. is embedded in the interiorportion of the membrane body, the reinforcing core material 10 would notdamage or stick out through the surface of the membrane body.Particularly, e.g., local peel off of the reinforcing core material 10can be effectively prevented. In this manner, the cation exchangemembrane 1 having a long life can be obtained.

In one aspect of the present embodiments, a, c and n preferably furthersatisfy the relationship of the following expression (3) in addition tothe relationship of expression (1) or expression (2).0.2a/(n+1)≦c≦0.9a/(n+1)  (3)

By satisfying the relationship of expression (3), the mechanicalstrength of the cation exchange membrane 1 can be further improved. Inaddition, the effect of reducing electrolysis voltage can be furtherimproved.

It is more preferable that a, c and n further satisfy the relationshipof expression (3-1) in addition to the relationship of expression (1) orexpression (2) and further preferable that a, c and n further satisfythe relationship of expression (3-2).0.4a/(n+1)≦c≦0.8a/(n+1)  (3-1)0.4a/(n+1)≦c≦0.75a/(n+1)  (3-2)

Furthermore, when the relationship of expression (3) is satisfied, a, band n preferably further satisfy the relationship of the followingexpression (4)a/(n+1)<b≦1.8a/(n+1)  (4)

By further satisfying the relationship of expression (4) in addition toexpression (3), the mechanical strength of the cation exchange membrane1 can be further improved. In addition, electrolysis voltage can befurther reduced.

In addition to expression (3), a, b and n more preferably satisfy therelationship of expression (4-1) and further preferably satisfy therelationship of expression (4-2).1.05a/(n+1)≦b≦1.6a/(n+1)  (4-1)1.1a/(n+1)≦b≦1.5a/(n+1)  (4-2)

Note that, in the interval between the reinforcing core materialssatisfying the relationships of expression (3) and expression (4), theinterval b between the elution holes and the reinforcing core materialsadjacent to each other is broad and the interval c between the elutionholes is narrow. That is, needless to say, expression (1) is satisfiedbetween the reinforcing core materials.

In addition, as the distance b between the reinforcing core materials 10and the elution holes 12 adjacent to each other, there are two distancesbetween the adjacent reinforcing core materials 10 (more specifically,in FIG. 2, one is present between the left end reinforcing core material10 and the elution holes 12 and the other is present between the rightend reinforcing core material 10 and the elution holes 12). Of the twob, at least one b may satisfy the relationship of expression (4). Morepreferably, both two b present between the adjacent reinforcing corematerials 10 satisfy the relationship of expression (4).

In another embodiment, a, c and n preferably further satisfy therelationship of the following expression (5) in addition to therelationship of expression (1) or expression (2).1.1a/(n+1)≦c≦0.8a  (5)

By satisfying the relationship of expression (5), the mechanicalstrength of the cation exchange membrane 1 can be further improved. Bysatisfying the relationship of expression (5), reduction of the tensileelongation of the cation exchange membrane 1 due to folding, etc. can befurther suppressed to further reduce electrolysis voltage.

More preferably, a, c and n satisfy the relationship of expression (5-1)in addition to the relationship of expression (1) or expression (2), andfurther preferably satisfy the relationship of expression (5-2).1.1a/(n+1)≦c≦1.8a/(n+1)  (5-1)1.1a/(n+1)≦c≦1.7a/(n+1)  (5-2)

In the expressions, taking the case where n=2 as an example, therelationship of the aforementioned expressions will be described. Whenn=2, the number of elution holes between the reinforcing core materialsis 2 and intervals are a/(n+1)=a/3 when elution holes are arranged atequal intervals. Therefore, when n=2, expression (1) and expression (2)become respectively the following expression (6) and expression (7).n=2,b>a/3  (6)n=2,c>a/3  (7)

Then, the intervals between the reinforcing core materials satisfyingthe relationship of expression (6) preferably further satisfy therelationship of expression (3). When the relationship of expression (3)is also satisfied in addition to expression (6), the interval betweenelution holes becomes narrow and the interval between the reinforcingcore material and the elution hole becomes wide. In this manner,mechanical strength improves and electrolysis voltage can be reduced.More preferably, expression (4) is also satisfied in addition toexpression (1).

Furthermore, the intervals between the reinforcing core materialssatisfying the relationship of expression (7) preferably further satisfythe relationship of expression (5). When the relationship of expression(5) is satisfied in addition to expression (7), the interval betweenelution holes becomes wide and the each interval between the reinforcingcore material and the elution hole becomes narrow. In this manner,mechanical strength improves and electrolysis voltage can be reduced.

More preferably, the first interval between the reinforcing corematerials satisfying the relationships of expression (6) and expression(3) and the second interval between the reinforcing core materialssatisfying the relationships of expression (7) and expression (5) arearranged alternately and repeatedly. In this arrangement, mechanicalstrength is further improved and electrolysis voltage can be reduced.

The cation exchange membrane according to the present embodiment issatisfactory as long as the relationship of expression (1) or expression(2) is satisfied in a predetermined direction of the membrane. Morespecifically, it is satisfactory as long as the relationship ofexpression (1) or expression (2) is satisfied in the direction of atleast either one of the MD direction and the TD direction of the cationexchange membrane. At least in the TD direction (TD yarn describedlater) of the cation exchange membrane, it is preferable to satisfy therelationship of expression (1) or expression (2), and more preferablyboth in the MD direction and in the TD direction of the cation exchangemembrane, the relationship of expression (1) or expression (2) issatisfied.

Then, in the direction of at least either one of the MD direction andthe TD direction, it is preferable to have the intervals between thereinforcing core materials satisfying the relationships of expression(3) and (4) in addition to the relationship of expression (1) orexpression (2); more preferable to have the intervals between thereinforcing core materials further satisfying the relationship ofexpression (3) at least in the TD direction (TD yarn) of the cationexchange membrane; and further preferable to have the intervals betweenthe reinforcing core materials further satisfying the relationship ofexpression (3) both in the MD direction and in the TD direction of thecation exchange membrane.

Furthermore, in the direction of at least either one of the MD directionand the TD direction, it is preferable to have the intervals between thereinforcing core materials satisfying the relationship of expression(5), in addition to expression (1) or expression (2); more preferable tohave the intervals between the reinforcing core materials furthersatisfying the relationship of expression (5) at least in the TDdirection (TD yarn) of the cation exchange membrane; and furtherpreferable to have the intervals between the reinforcing core materialsfurther satisfying the relationship of expression (5) both in the MDdirection and in the TD direction of the cation exchange membrane.

The MD direction (machine direction) used herein refers to the directionalong which the membrane body and various core materials (for example, areinforcing material obtained in the case where the reinforcing materialis woven by using a reinforcing core material, a reinforcing yarn, asacrifice yarn, a dummy yarn, etc.) are transported (“feed direction”)in the process for producing the cation exchange membrane as describedlater. Furthermore, the MD yarn refers to a yarn woven (knitted) alongthe MD direction. The TD direction (transverse direction) refers to thedirection in generally perpendicular to the MD direction. Furthermore,the TD yarn refers to a yarn woven (knitted) along the TD direction. Ifnot only the relationship of expression (1) or expression (2) but alsoexpression (3) or expression (5) etc., is satisfied in two directions,i.e., the MD direction and the TD direction of the cation exchangemembrane, mechanical strength of the cation exchange membrane can befurther improved and electrolysis voltage can be further reduced.

FIG. 3 is a conceptual diagram of the second embodiment of the cationexchange membrane according to the present embodiment. A cation exchangemembrane 2 satisfies the relationship of expression (1) or expression(2) both in the MD direction and in the TD direction. More specifically,the cation exchange membrane 2 at least has two or more reinforcing corematerials 20 x arranged within the membrane body in the MD direction(see X) of the membrane body (not shown) and two or more elution holes22 x are formed between the reinforcing core materials 20 x adjacent toeach other. Assuming that the distance between the reinforcing corematerials 20 x adjacent to each other is represented by a_(x), thedistance between the reinforcing core materials 20 x and the elutionholes 22 x adjacent to each other is represented by b_(x), the distancebetween the elution holes 12 adjacent to each other is represented byc_(x), and the number of the elution holes 22 x formed between thereinforcing core materials 20 x adjacent to each other is represented byn_(x), then the relationship represented by the following expression(1x) or expression (2x) is satisfied.b _(x) >a _(x)/(n _(x)+1)  (1x)c _(x) >a _(x)/(n _(x)+1)  (2x)

Furthermore, the cation exchange membrane 2 has at least two or morereinforcing core materials 20 y arranged within the membrane body in theTD direction (see Y) of the membrane body (not shown) and two or moreelution holes 22 y are formed between the reinforcing core materials 20y adjacent to each other. Assuming that the distance between thereinforcing core materials 20 y adjacent to each other is represented bya_(y), the distance between the reinforcing core materials 20 y and theelution holes 22 y adjacent to each other is represented by b_(y), thedistance between the adjacent elution holes 12 is represented by c_(y),and the number of the elution holes 22 y formed between the adjacentreinforcing core materials 20 y is represented by n_(y), then therelationship represented by the following expression (1y) or expression(2y) is satisfied.b _(y) >a _(y)/(n _(y)+1)  (1y)c _(y) >a _(y)/(n _(y)+1)  (2y)

In the present embodiment, it is not necessary that all reinforcing corematerials and elution holes in the cation exchange membrane are formedso as to satisfy the aforementioned specific relationship (for example,expression (1) or expression (2), or expression (3) or expression (5) orthe like). For example, if the cation exchange membrane has at least oneinterval between the reinforcing core materials having elution holesarranged so as to satisfy the relationship of expression (1) orexpression (2), folding resistance of the cation exchange membrane isimproved.

Furthermore, assuming that the region partitioned by adjacent tworeinforcing core materials in the MD direction of the cation exchangemembrane and adjacent two reinforcing core materials in the TD directionthereof is specified as one region, the ratio of the area of regionssatisfying the relationship of expression (1) or expression (2) relativeto the area of all regions in the cation exchange membrane is notparticularly limited; however, it is preferably from 80 to 100% and morepreferably from 90 to 100%. The edge periphery of the cation exchangemembrane is to be immobilized in the electrolysis vessel while using andused as a site sandwiched by e.g., flanges of the electrolysis vessel.If the area ratio is 80% or more, in a portion corresponding to acurrent-carrying portion, formation of e.g., pinholes and cracks byfolding can be prevented. For this reason, the area ratio of 80% or moreis preferable. In addition, if the area ratio is 80% or more, in theportion corresponding to a current-carrying portion, an effect ofreducing electrolysis voltage can be obtained. For this reason, the arearatio of 80% or more is preferable.

Furthermore, when the relationship of expression (3) or expression (5)is satisfied, the area ratio of regions satisfying the relationship ofexpression (3) or expression (5) is not particularly limited; however,it is preferably from 40 to 100% relative to the area of all regions inthe cation exchange membrane and more preferably from 45 to 100%. In theregion satisfying the relationship of expression (3) or expression (5),folding resistance tends to be further superior, compared to the regionalso satisfying expression (1) or expression (2). Therefore, if the arearatio is 40% or more, sufficiently high folding resistance can beobtained.

FIG. 4 is a conceptual diagram of the third embodiment of the cationexchange membrane according to the present embodiment. A cation exchangemembrane 3 is a cation exchange membrane at least having a membrane body(not shown) containing a fluorine-based polymer having an ion-exchangegroup and two or more reinforcing core materials 301, 302, 303 arrangedapproximately in parallel within the membrane body, and 2 sets or more nnumber of elution holes 321, 322, 323, . . . , 324, 325, 326, . . . areformed between the reinforcing core materials adjacent to each other.

In the case of FIG. 4, the interval between the reinforcing corematerials separated by the reinforcing core materials 301 and 302 andthe interval between the reinforcing core materials separated by thereinforcing core materials 302 and 303 are arranged alternately andrepeatedly. More specifically, in the interval between the reinforcingcore materials separated by the reinforcing core materials 301 and 302,the elution holes 321, 322, 323 are formed at the distance c₁, c₂, . . .(hereinafter sometimes collectively referred to as c). Of these, atleast c₁ satisfies the relationship of expression (2): c₁>a₁/(n+1). Incontrast, in the interval between the reinforcing core materialsseparated by the reinforcing core materials 302 and 303, the interval b₂between the reinforcing core materials and the elution holes adjacent toeach other at least satisfies the relationship of expression (1):b₂>a₁/(n+1).

As described above, in the cation exchange membrane, it is preferablethat the first interval between the reinforcing core materials (theinterval separated by the reinforcing core material 302 and thereinforcing core material 303) satisfying the relationship of expression(1) and the second interval between the reinforcing core materials (theinterval separated by the reinforcing core material 301 and thereinforcing core material 302) satisfying the relationship of expression(2) alternately appear. Owing to this arrangement, mechanical strengthof the cation exchange membrane 3 can be further improved in thedirection and electrolysis voltage thereof can be further reduced.

Note that, in the present embodiment, the direction along which thefirst region and the second region above are alternately arranged in thecation exchange membrane is not particularly limited; however, in atleast either the MD direction or the TD direction of the cation exchangemembrane, the first interval between the reinforcing core materialssatisfying the relationship of expression (1) and the second intervalbetween the reinforcing core materials satisfying the relationship ofexpression (2) are alternately arranged. The cation exchange membranehaving such arrangement is preferable. More preferably, the cationexchange membrane has the first interval between the reinforcing corematerials satisfying the relationship of expression (1) and the secondinterval between the reinforcing core materials satisfying therelationship of expression (2), which are alternately and repeatedlyarranged along the MD direction (TD yarn arrangement direction) of thecation exchange membrane. Further preferably, the cation exchangemembrane has the first interval between the reinforcing core materialssatisfying the relationship of expression (1) and the second intervalbetween the reinforcing core materials satisfying the relationship ofexpression (2), which are alternately and repeatedly arranged along theMD direction and the TD direction.

Generally, the cation exchange membrane has a rectangular shape. In mostcases, its longitudinal direction corresponds to the MD direction andits transverse direction corresponds to the TD direction. Such thecation exchange membrane is wound around a tubular body like a vinylchloride tube to transport at the time of shipment and during a leadtime until installation into an electrolysis vessel. When the membraneis wound around the tubular body, the cation exchange membrane issometimes folded in the TD direction to reduce the length of the tubularbody. Even in such the case, concentration of load in the TD directioncan be efficiently avoided as long as the cation exchange membranecontained as mentioned above is used, and thus formation of a pinhole,etc., can be effectively prevented.

As one aspect of the present embodiments, the cation exchange membranepreferably has the first interval between the reinforcing core materialssatisfying the relationship of expression (1), which further satisfiesthe relationships of expressions (3) and (4) and the second intervalbetween the reinforcing core materials satisfying the relationship ofexpression (2), which further satisfies the relationship of expression(5). Owing to this arrangement, mechanical strength can be furtherimproved and electrolysis voltage can be further reduced. Note that,even in this case, the direction along which the first region and thesecond region above are alternately arranged in the cation exchangemembrane is not particularly limited.

Furthermore, as another embodiment, the ion exchange membrane preferablyhas the first interval between the reinforcing core materials satisfyingthe relationship of expression (1) which further satisfies therelationship of expression (6) and the second interval between thereinforcing core materials satisfying the relationship of expression (2)which further satisfies the relationship of expression (7). Owing tothis arrangement, mechanical strength can be further improved andelectrolysis voltage can be further reduced. Note that, even in thiscase, the direction along which the first region and the second regionabove are alternately arranged in the cation exchange membrane is notparticularly limited.

FIG. 5 is a conceptual diagram of the fourth embodiment of the cationexchange membrane according to the present embodiment. A cation exchangemembrane 4 is a cation exchange membrane at least having a membrane body(not shown) containing a fluorine-based polymer having an ion-exchangegroup and two or more reinforcing core materials 401, 402, 403 arrangedapproximately in parallel within the membrane body, in which, in atleast either one of the directions, i.e., in the MD direction or in theTD direction, of the cation exchange membrane 4, the interval betweenthe reinforcing core materials satisfying the relationship of thefollowing expression (6) and the interval between the reinforcing corematerials satisfying the relationship of the following expression (7)are alternately present.n=2,b>a/3  (6)n=2,c>a/3  (7)

Such an arrangement is preferable because mechanical strength can befurther improved and electrolysis voltage can be further reduced by thearrangement.

In FIG. 5, in the interval separated by the reinforcing core material401 and the reinforcing core material 402, the distance b₁ between thereinforcing core material 401 and the elution hole 421 and the distanceb₂ between the reinforcing core material 402 and the elution hole 422both satisfy the relationship of the above expression (6): b₁ (b₂)>a/3.Furthermore, the distance c₁ between two elution holes 421 and 422satisfies the relationship: c₁<a₁/3. In other words, in the intervalseparated by the reinforcing core material 401 and the reinforcing corematerial 402, the distance c₁ between two elution holes 421 and 422 isnarrow compared to the distance between them in which they are arrangedat an equal interval.

Note that, in the expression (6), it is satisfactory if at least eitherone of b₁ or b₂ satisfies the relationship of b>a/3, however in view ofmechanical strength and convenience in production, it is more preferablethat b₁ and b₂ both satisfy the relationship: b>a/3.

In the interval separated by the reinforcing core material 402 and thereinforcing core material 403, the distance b₃ between the reinforcingcore material 402 and the elution hole 423 and the distance b₄ betweenthe reinforcing core material 403 and the elution hole 434 both satisfythe relationship: b<a₂/3. Furthermore, the distance c₂ between twoelution holes 423 and 424 satisfies the relationship of the expression(7): c₂>a₂/3. In other words, in the interval separated by thereinforcing core material 402 and the reinforcing core material 403, thedistance c₂ between two elution holes 423 and 424 is wide compared tothe distance between them in which they are arranged at an equalinterval.

Note that, if the relationship of expression (7) above is satisfied, atleast either one of b₃ or b₄ may satisfy the relationship: b<a/3;however, it is preferable that, in view of mechanical strength andconvenience in production, b₃ and b₄ both satisfy the relationship:b<a/3.

In at least either one of the directions, i.e., the MD direction or theTD direction of the cation exchange membrane 4, it is more preferablethat the interval between reinforcing core materials satisfying therelationship of the following expression (8) and the interval betweenreinforcing core materials satisfying the relationship of the followingexpression (9) are alternately present. In this case, in FIG. 5,distances a₁, b₁, b₂, and c₁ satisfy the relationship of the followingexpression (8); and distances a₂, b₃, b₄, and c₂ satisfy therelationship of the following expression (9).n=2,0.2a/3≦c≦0.9a/3,a/3<b≦1.8a/3  (8)n=2,1.1a/3≦c≦0.8  (9)

Owing to this arrangement, mechanical strength can be further improvedand electrolysis voltage can be further reduced.

FIG. 6 is a conceptual diagram of the fifth embodiment of the cationexchange membrane according to the present embodiment. In a cationexchange membrane 5, 4 regions are formed, which are partitioned byreinforcing core materials 501 x, 502 x, 503 x arranged along the MDdirection (see X) and reinforcing core materials 501 y, 502 y, 503 yarranged along the TD direction (see Y). Furthermore, elution holes 521x, 522 x, 523 x, 524 x are formed along the MD direction of the cationexchange membrane 5 and elution holes 521 y, 522 y, 523 y, 524 y areformed along the TD direction. Moreover, the cation exchange membrane 5has a structure having a region where the intervals between elutionholes are less densely arranged and a region where the intervals betweenelution holes are densely arranged are alternately arranged in both theMD direction and in the TD direction.

The cation exchange membrane 5 has (i) a first region surrounded by thereinforcing core materials 501 x, 502 x in the MD direction and thereinforcing core materials 501 y, 502 y in the TD direction, (ii) asecond region surrounded by the reinforcing core materials 502 x, 503 xin the MD direction and the reinforcing core materials 501 y, 502 y inthe TD direction; (iii) a third region surrounded by the reinforcingcore materials 502 x, 503 x in the MD direction and the reinforcing corematerials 501 y, 502 y in the TD direction and (iv) a fourth regionsurrounded by the reinforcing core materials 502 x, 503 x in the MDdirection and the reinforcing core materials 502 y, 503 y in the TDdirection. These regions are repeatedly arranged.

In the first region, the elution holes 521 x, 522 x are arranged in theMD direction so as to satisfy the relationship of expression (6) and theelution holes 521 y, 522 y are arranged in the TD direction so as tosatisfy the relationship of expression (7). Since mechanical strengthcan be further improved and electrolysis voltage can be further reduced,the elution holes 521 x, 522 x are preferably arranged in the MDdirection so as to satisfy the relationship of expression (8). Owing tothis arrangement, mechanical strength of the cation exchange membranecan be further improved and electrolysis voltage thereof can be furtherreduced. Similarly, the elution holes 521 y, 522 y are preferablyarranged in the TD direction so as to satisfy the relationship ofexpression (9).

In the second region, the elution holes 523 x, 524 x are arranged in theMD direction so as to satisfy the relationship of expression (7) and theelution holes 521 y, 522 y are arranged in the TD direction so as tosatisfy the relationship of expression (7). In the MD direction, theelution holes 523 x, 524 x are preferably arranged so as to satisfy therelationship of expression (9). Owing to this arrangement, mechanicalstrength of the cation exchange membrane can be further improved andelectrolysis voltage thereof can be further reduced. Similarly, theelution holes 521 y, 522 y are preferably arranged in the TD directionso as to satisfy the relationship of expression (9).

In the third region, the elution holes 521 x, 522 x are arranged in theMD direction so as to satisfy the relationship of expression (6) and theelution holes 523 y, 524 y are arranged in the TD direction so as tosatisfy the relationship of expression (6). In the MD direction, theelution holes 521 x, 522 x are preferably arranged so as to satisfy therelationship of expression (8). Owing to this arrangement, mechanicalstrength of the cation exchange membrane can be further improved andelectrolysis voltage thereof can be further reduced. Similarly, theelution holes 523 y, 524 y are preferably arranged in the TD directionso as to satisfy the relationship of expression (8).

In the fourth region, the elution holes 523 x, 524 x are arranged in theMD direction so as to satisfy the relationship of expression (7) and theelution holes 523 y, 524 y are arranged in the TD direction so as tosatisfy the relationship of expression (6). In the MD direction, theelution holes 523 x, 524 x are preferably arranged so as to satisfy therelationship of expression (9). Owing to this arrangement, mechanicalstrength of the cation exchange membrane can be further improved andelectrolysis voltage thereof can be further reduced. Similarly, theelution holes 523 y, 524 y are preferably arranged in the TD directionso as to satisfy the relationship of expression (8).

Owing to the aforementioned structure, balance of arrangement of thereinforcing core materials and the elution holes in the cation exchangemembrane can be further improved, with the result that the dimensionalstability can be further improved.

<Producing Method>

A method for producing a cation exchange membrane according to thepresent embodiment, comprising the steps of:

weaving two or more reinforcing core materials, a sacrifice yarn solublein an acid or an alkali, and a dummy yarn having a property ofdissolving in a predetermined solvent in which the reinforcing corematerials and the sacrifice yarn are insoluble, to obtain a reinforcingmaterial having the sacrifice yarn and the dummy yarn arranged betweenthe reinforcing core materials adjacent to each other;

soaking the reinforcing material in the predetermined solvent to removethe dummy yarn from the reinforcing material;

stacking the reinforcing material from which the dummy yarn is removedand a fluorine-based polymer having an ion-exchange group or anion-exchange group precursor which can be converted into theion-exchange group by hydrolysis, to form a membrane body having thereinforcing material; and

soaking the sacrifice yarn in an acid or an alkali to remove thesacrifice yarn from the membrane body, thereby forming an elution holein the membrane body.

One of the characteristics of the present embodiment resides in that theintervals of the elution holes formed between the reinforcing corematerials adjacent to each other (see, for example, FIG. 2 b, c) are notequally separated. In order to easily and efficiently realize such thestructure, a dummy yarn can be used. This will be more specificallydescribed with reference to FIG. 7.

FIG. 7 is a conceptual diagram for illustrating a producing methodaccording to the present embodiment. First, between two or morereinforcing core materials 60, sacrifice yarns 62 for forming elutionholes and dummy yarns 66 are woven to obtain a reinforcing material 6(see FIG. 7, (i)). The reinforcing material 6 can be obtained as aso-called woven fabric and a knitted fabric etc. Note that, in view ofproductivity, a woven fabric is preferable. In this case, between thereinforcing core materials 60, the sacrifice yarns 62 and the dummyyarns 66 are preferably woven so as to be arranged at approximatelyequal intervals (interval d). By weaving the sacrifice yarns 62 and thedummy yarns 66 at approximately equal intervals, no complicated controlis required to arrange the sacrifice yarns 62 at the intervals whichsatisfy relational expression of expression (1) and expression (2),etc., and an operation for weaving yarns can be simply performed with asatisfactory production efficiency. Note that, the dummy yarn 66 has ahigh solubility to a predetermined solvent.

Then, the reinforcing material 6 is soaked in a predetermined solvent toselectively dissolve and remove the dummy yarn 66 alone (see FIG. 7(ii)). Owing to this step, the site where the dummy yarns 66 have beenwoven becomes a vacant space and thus the interval is widened.

The type of the predetermined solvent for dissolving and removing thematerial for the dummy yarn 66 and dummy yarn 66 is not particularlylimited; however, it is satisfactory if the solubility of the dummy yarnto the predetermined solvent is higher than that of the reinforcing corematerial 60 and the sacrifice yarn 62. Examples of the material for thedummy yarn 66 may include polyvinyl alcohol (PVA), rayon, polyethyleneterephthalate (PET), cellulose and polyamide. Of these, polyvinylalcohol is preferable in view of high solubility.

As the predetermined solvent, any solvent may be used as long as it doesnot dissolve a reinforcing core material and a sacrifice yarn but candissolve a dummy yarn. Therefore, the amount, etc. of solvent requiredfor dissolving the dummy yarn is not particularly limited; however, thekind and amount of solvent can be appropriately selected inconsideration of the quality of the reinforcing core material, sacrificeyarn, dummy yarn to be used and producing conditions, etc. Examples ofsuch a solvent may include an acid, an alkali and hot water. Examples ofthe acid may include hydrochloric acid, nitric acid and sulfuric acid.Examples of the alkali may include sodium hydroxide and potassiumhydroxide. Of these, sodium hydroxide or hot water is preferable in viewof high dissolution rate.

The thickness and shape, etc. of the dummy yarn 66 are not particularlylimited; however, a yean formed of from 4 to 12 polyvinyl alcoholfilaments having a thickness of from 20 to 50 deniers and a circularcross-section is preferable.

The sacrifice yarn 62 refers to a yarn capable of dissolving in an acidor an alkali to form an elution hole in the cation exchange membrane. Inaddition, the solubility of the sacrifice yarn 62 in a predeterminedsolvent in which the dummy yarn 66 dissolves is lower than that of thedummy yarn 66. Examples of the material for the sacrifice yarn 62 mayinclude polyvinyl alcohol (PVA), rayon, polyethylene terephthalate(PET), cellulose and polyamide. Of these, polyethylene terephthalate(PET) is preferable in view of stability during a weaving step andsolubility to an acid or an alkali.

The amount of the sacrifice yarn 62 contained in a fabric is preferablyfrom 10 to 80 mass % based on the total amount of the reinforcingmaterial and more preferably from 30 to 70 mass %. Furthermore, thesacrifice yarn has a thickness of from 20 to 50 deniers and preferablyformed of a monofilament or multifilament.

The dummy yarn 66 can be woven such that it inserts between sacrificeyarns 62 and between the reinforcing core material 60 and the sacrificeyarn 62. Therefore, the intervals of the reinforcing core materials 60and the sacrifice yarns 62 arranged in the reinforcing material 6 can bearbitrarily determined by appropriately selecting the thickness andshape of the dummy yarn and the manner and order of weaving the dummyyarn. Since the dummy yarn 66 is removed by a predetermined solventbefore the reinforcing material 6 is layered on a fluorine-basedpolymer, the interval of the sacrifice yarns 62 to be arranged can bearbitrarily determined. In this manner, the reinforcing core material 60and the sacrifice yarn 62 for forming an elution hole can be arranged soas to satisfy the relationship of expression (1) or expression (2).

Furthermore, as to the MD yarn, although not shown in the figure, thesacrifice yarn, etc. can be arranged at arbitrary intervals in thereinforcing material by a method of passing a bundle of two or moreyarns selected from the reinforcing yarn, the sacrifice yarn and thedummy yarn through a single dent of the reed of the weaving machine or amethod of providing a dent having no yarn between dents through which areinforcing yarn, a sacrifice yarn, a dummy yarn, etc. are passed. Forexample, control in the MD direction can be made by varying types ofyarns (reinforcing yarn, sacrifice yarn, etc.) used in combinationpassing through a single dent of the reed of a weaving machine. Morespecifically, a bundle of a reinforcing yarn and a sacrifice yarn ispassed through a first dent, a bundle of a sacrifice yarn and areinforcing yarn is passed through a second yarn, a sacrifice yarn and asacrifice yarn are passed through a third bundle. In this case, thearrangement of a reinforcing yarn, a sacrifice yarn, a sacrifice yarn, areinforcing yarn, a sacrifice yarn and a sacrifice yarn in this ordercan be repeatedly made. In this manner, the intervals of the sacrificeyarn arranged in a reinforcing material can be controlled.

Subsequently, the reinforcing material 6 from which a dummy yarn 66 isremoved is layered on a fluorine-based polymer having an ion-exchangegroup to form a membrane body having the reinforcing material 6. Apreferable method for forming the membrane body may include, forexample, a method having the following (1) step and (2) step.

(1) A fluorine-based polymer layer (hereinafter referred to as a “firstlayer”) containing a carboxylate functional group positioned on thecathode side and a fluorine-based polymer layer (hereinafter referred toas a “second layer”) containing a sulfonyl fluoride functional group arecoextruded to form a film. Subsequently, the reinforcing material andthe second layer/first layer composite film are layered in this order ona flat-plate or a drum having a heat source and a vacuum source, andhaving micro pores in the surface, via a permeable heat resistantrelease paper. These films are integrated at the temperature under whichindividual polymers melt while removing air between the layers byreducing pressure.

(2) Separately from the second layer/first layer composite film, afluorine-based polymer layer (hereinafter referred to as a “thirdlayer”) containing a sulfonyl fluoride functional group is singly formedinto a film in advance. Subsequently, the third layer film, reinforcingmaterial and second layer/first layer composite film are layered in thisorder on a flat-plate or a drum having a heat source and a vacuum sourceand having micro pores in the surface, via a permeable heat resistantrelease paper. These films are integrated at the temperature under whichindividual polymers melt while removing air between the layers byreducing pressure. Note that, in this case, the direction along whichthe extruded film is fed is the MD direction.

Coextruding the first layer and the second layer in the step (1)contributes to enhancing the adhesion strength of the interface.Furthermore, in the integration method under reduced pressure, comparedto a pressurizing press method, the thickness of the third layer on thereinforcing material characteristically increases. Moreover, since thereinforcing material is immobilized within the cation exchange membrane,mechanical strength of the cation exchange membrane can be sufficientlymaintained.

Note that, to further increase the durability of the cation exchangemembrane, a layer (hereinafter referred to as a “fourth layer”)containing both a carboxylate functional group and a sulfonyl fluoridefunctional group can be further interposed between the first layer andthe second layer and a layer containing both a carboxylate functionalgroup and a sulfonyl fluoride functional group can be used as the secondlayer. In this case, a method in which a polymer containing acarboxylate functional group and a polymer containing a sulfonylfluoride functional group are separately produced and then mixed, and amethod in which a monomer containing a carboxylate functional group anda monomer containing a sulfonyl fluoride functional group both arecopolymerized and put in use may be used.

In the case where the fourth layer is used as a constitutional elementof the cation exchange membrane, the first layer and the fourth layermay be formed into a coextrusion film, the second layer and the thirdlayer may be separately and singly formed into films, and then thesefilms may be layered in accordance with the aforementioned method.Furthermore, the three layers, i.e., first layer, fourth layer andsecond layer, may be simultaneously coextruded into a film. In thismanner, a membrane body containing a fluorine-based polymer having anion-exchange group can be formed on the reinforcing material.

Furthermore, the sacrifice yarn contained in the membrane body isremoved by dissolving it in an acid or an alkali to form elution hole(s)in the membrane body. The sacrifice yarn has a solubility to an acid oran alkali and the sacrifice yarn is eluted in the cation exchangemembrane producing step and under the electrolysis environment to formelution holes at the elution sites. In this manner, the cation exchangemembrane having elution holes formed in the membrane body can beobtained. The elution holes are formed with positional relationshipsatisfying the aforementioned relational expression represented byexpression (1) or expression (2).

Furthermore, the cation exchange membrane according to the presentembodiment preferably has a protruding portion only consisting ofpolymer having an ion-exchange group on the sulfonic acid layer side (onthe anode surface side, see FIG. 1). The protruding portion ispreferably consisting of resin alone. The protruding portion can beformed by previously embossing the release paper which can be used inintegrating the aforementioned composite film of the second layer andthe first layer and the reinforcing material, etc.

The cation exchange membrane according to the present embodiment can beused in various electrolysis vessels. FIG. 10 is a conceptual diagram ofthe electrolysis vessel according to the present embodiment. Anelectrolysis vessel A at least has an anode A1, a cathode A2 and thecation exchange membrane 1 according to the present embodiment arrangedbetween the anode A1 and the cathode A2. The electrolysis vessel A canbe used for various types of electrolysis. Hereinbelow, as a typicalexample, the case where the cation exchange membrane is used inelectrolysis for an aqueous alkali chloride solution will be described.

Electrolysis conditions are not particularly limited; however,electrolysis can be performed in conventionally known conditions. Forexample, a 2.5 to 5.5 N aqueous alkali chloride solution is supplied toan anode chamber, whereas water or a diluted aqueous alkali hydroxidesolution is supplied to a cathode chamber. Electrolysis can be performedin the conditions: a temperature of from 50 to 120° C. and a currentdensity of from 5 to 100 A/dm².

The constitution of the electrolysis vessel according to the presentembodiment is not particularly limited; for example, a unipolar systemor a multipolar system may be employed. The materials for constitutingthe electrolysis vessel are not particularly limited. For example, as amaterial for the anode chamber, alkali chloride and chlorine-resistanttitanium are preferable. As a material for the cathode chamber, e.g.,alkali hydroxide and hydrogen-resistant nickel are preferable. As thearrangement of electrodes, an appropriate interval may be providedbetween the cation exchange membrane and the anode. However if the anodeis arranged in contact with the ion exchange membrane, this structurecan be used without any problem. Furthermore, the cathode is generallyarranged at an appropriate interval with the cation exchange membrane.However, a contact-type electrolysis vessel (zero-gap systemelectrolysis vessel) having no interval between them can be used withoutany problem.

In the cation exchange membrane according to the present embodiment,electrolysis voltage can be reduced by arranging membrane-constitutingmembers within the membrane body so as to satisfy the aforementionedrelational expressions. Particularly, compared to a conventional cationexchange membrane where elution holes for passing various substancessuch as a cation are arranged at equal intervals, resistance to a cationdecreases by arranging elution holes at unequal intervals. As a result,electrolysis voltage may presumably decrease (note that, the function ofthe present embodiment is not limited to this).

Particularly, in the intervals between reinforcing core materialssatisfying the relationship of aforementioned expression (2), elutionholes are arranged near a reinforcing core material interrupting acation. Owing to the arrangement, the region interrupting a cationreduces and the resistance to a cation further reduces. As a result,electrolysis voltage is further reduced (note that, the function of thepresent embodiment is not limited to this).

EXAMPLES

Hereinbelow, the present invention will be more specifically describedby way of Examples. Note that, the present invention is not limited tothe following Examples.

[Measurement of Distance]

The distance a between the reinforcing core materials adjacent to eachother, distance b (b₁, b₂) between the reinforcing core materials andelution holes adjacent to each other, and the distance c (c₁, c₂)between the elution holes adjacent to each other were measured by thefollowing methods (see FIGS. 8 and 9).

In the case where the distance in the TD direction was measured, thecation exchange membrane was cut along the direction in perpendicular tothe TD direction (i.e., the MD direction). The cut surface was a crosssection of the cation exchange membrane in the TD direction. In the casewhere the distance in the MD direction was measured, the cation exchangemembrane was cut along the direction in perpendicular to the MDdirection (the TD direction). The cut surface was a cross section of thecation exchange membrane in the MD direction.

The cross section of the cation exchange membrane was magnified by amicroscope and a, b and c in the TD direction and in the MD directionwere measured. At this time, the distance was determined by measuringthe distance between the center point of the reinforcing core materialand the center point of the elution hole in the transverse direction.For example, a was determined by measuring the distance between thecenter point of the reinforcing core material and the center point ofthe other adjacent reinforcing core material in the transversedirection. Note that, a, b and c were measured 5 times and an averagevalue of the 5 measurement values was used.

[Measurement of Folding Resistance]

Degree of reduction in strength (folding resistance) by folding thecation exchange membrane was evaluated by the following method. Notethat, the folding resistance refers to the ratio of the tensileelongation (tensile elongation ratio) of the cation exchange membraneafter folding relative to the tensile elongation of the cation exchangemembrane before folding.

Tensile elongation was measured by the following method. A sample of 1cm in width was cut along the direction having an angle of 45 degreesagainst the reinforcing yarn embedded in the cation exchange membrane.Subsequently, the tensile elongation of the sample was measured in theconditions: the distance between chucks: 50 mm, a tension rate: 100mm/minute in accordance with JIS K6732.

The cation exchange membrane was folded by the following method. Thecation exchange membrane was folded by applying weight of 400 g/cm² soas to allow the surface of the carboxylic acid layer side (see FIG. 1,the carboxylic acid layer 144, and “polymer A layer” described later) toface inside. In the MD-folding, the cation exchange membrane was foldedso as to form a folding line in perpendicular to the MD yarn of thecation exchange membrane and evaluation was made (MD folding). In the TDfolding, the cation exchange membrane was folded so as to form a foldingline in perpendicular to the TD yarn of the cation exchange membrane andevaluation was made (TD folding). Therefore, in the MD folding,contribution of control of intervals between reinforcing core materialsand elution holes arranged along the TD direction to folding resistancecan be evaluated, whereas in the TD folding, contribution of control ofintervals between reinforcing core materials and elution holes arrangedalong the MD direction to folding resistance can be evaluated.

After MD folding and TD folding were separately made, tensile elongationof the cation exchange membrane was measured to obtain a ratio oftensile elongation relative to that before folding. This ratio wasemployed as a folding resistance.

[Measurement of Electrolysis Voltage]

An electrolysis vessel was prepared using the cation exchange membraneand its electrolysis voltage was measured. The electrolysis voltage wasmeasured in an electrolysis cell of a forced circulation type having a1.5 mm-gap. As the cathode, an electrode formed by applying nickel oxideserving as a catalyst onto a nickel expanded metal was used. As theanode, an electrode formed by applying ruthenium, iridium and titaniumserving as a catalyst onto a titanium expanded metal was used. In theelectrolysis cell, the cation exchange membrane was arranged between theanode chamber and the cathode chamber.

To the anode side, an aqueous sodium chloride solution was suppliedwhile controlling a concentration to be 205 g/L, whereas water wassupplied while maintaining the caustic soda concentration on the cathodeside at 32 wt %. Subsequently, electrolysis was performed for 7 days ata current density of 80 A/dm² and a temperature of 90° C., in theconditions that liquid pressure on the cathode side of the electrolysisvessel was set to be higher by 5.3 kPa than the liquid pressure of theanode side. Thereafter, the electrolysis voltage required was measuredby a voltmeter.

Example 1

As a reinforcing core material, a monofilament ofpolytetrafluoroethylene (PTFE) of 90 deniers (hereinafter referred to asa “PTFE yarn”) was used. As a sacrifice yarn, a yarn of 6-filamentpolyethylene terephthalate (PET) of 40 deniers twisted at a rate of 200times/m (hereinafter referred to as a “PET yarn”) was used. As a dummyyarn, a yarn of 15-filament polyvinyl alcohol (PVA) of 36 denierstwisted at a rate of 200 times/m (hereinafter referred to as a “PVAyarn”) was used.

First, PTFE yarns were arranged at a rate of 24 yarns/inch atapproximately equal intervals. MD yarns were prepared by use of acontinuous 3-dent reed as follows. A bundle of 2 yarns consisting ofPTFE yarn and PET yarn was passed through a first reed; a bundle of 2yarns consisting of PET yarn and PTFE yarn was passed through a secondreed; and a bundle of 2 yarns consisting of PET yarn and PET yarn waspassed through a third reed. The bundles of yarns in this combinationwere sequentially and repeatedly passed through the reed in this order.As to TD yarns, PTFE yarn, PET yarn, PVA yarn, PVA yarn, PET yarn, PTFEyarn, PVA yarn, PVA yarn, PET yarn, PET yarn, PVA yarn and PVA yarn werearranged in this order repeatedly and at approximately equal intervalsto obtain a plain weave. In this manner, a woven fabric (reinforcingmaterial) was obtained. Subsequently, the obtained reinforcing materialwas subjected to contact bonding performed by a roll heated to 125° C.Thereafter, the reinforcing material was soaked in a 0.1 N aqueoussodium hydroxide solution to dissolve a dummy yarn (PVA yarn) alone andremove it from the reinforcing material. The thickness of thereinforcing material from which the dummy yarn was removed was 81 μm.

Next, dry-resin polymer A, which was a copolymer of tetrafluoroethylene(CF₂=CF₂) and CF₂=CFOCF₂CF(CF₃)OCF₂CF₂COOCH₃ and had a total ionexchange capacity of 0.85 mg equivalent/g, and a dry-resin polymer B,which was a copolymer of CF₂=CF₂ and CF₂=CFOCF₂CF(CF₃)OCF₂CF₂SO₂F andhad a total ion exchange capacity of 1.05 mg equivalent/g, wereprepared. Using polymers A and B, two-layered film X, which consisted ofa polymer A layer of 13 μm in thickness and a polymer B layer of 84 μmin thickness, was obtained in accordance with a coextrusion T-diemethod. Furthermore, film Y consisting of a polymer B of 20 μm inthickness was obtained by using a single layer T-die method.

Subsequently, release paper, film Y, a reinforcing material and film Xwere layered in this order on a drum housing a heat source and a vacuumsource and having micro pores in the surface, and heated under reducedpressure. At this time, the processing temperature was 219° C. and adegree of pressure reduction was 0.022 MPa. Thereafter, the releasepaper was removed to obtain composite film. The obtained composite filmwas soaked in an aqueous solution containing 30 mass % of dimethylsulfoxide (DMSO) and 15 mass % of potassium hydroxide (KOH) at 90° C.for 1 hour to perform hydrolysis, followed by washing with water anddrying. In this manner, the sacrifice yarn (PET yarn) was dissolved toobtain a membrane body having elution holes formed therein.

Furthermore, to a 5 mass % ethanol solution of an acid-type polymer,polymer B, zirconium oxide having a primary particle size of 1 μm wasadded up to a faction of 20 mass %, and dispersed to prepare asuspension solution. The suspension solution was sprayed to bothsurfaces of the above composite film by a spray method and dried to forma coating layer (0.5 mg/cm²) on the surfaces of the composite film. Inthis manner, the cation exchange membrane 7 as shown in FIG. 8 wasobtained. The cation exchange membrane 7 of FIG. 8 had a membrane body(not shown) and two or more reinforcing core materials 70 arrangedapproximately in parallel within the membrane body. The membrane bodyhad a structure where two elution holes 72 were formed between thereinforcing core materials 70 adjacent to each other. In the structureof Example 1, the intervals between reinforcing core materials havinga₁, b₁, c₁ and the intervals between reinforcing core materials havinga₂, b₂, c₂ repeatedly appear in the TD direction or in the MD direction.Note that, in other Examples and Comparative Examples described later,if the intervals between reinforcing core materials have only single a,b, c values in the TD direction or in the MD direction, these valueswill be hereinafter described as a₁, b₁, c₁.

In the obtained cation exchange membrane, in the TD direction, thedistance a₂ between the reinforcing core materials adjacent to eachother was 1112 μm, the number n of elution holes provided between theadjacent reinforcing core materials was 2 and the distance c₂ betweenthe adjacent elution holes was 432 μm. According to calculation,distance c₂ was expressed by 1.17a₂/(n+1) (see FIG. 8, the samehereinafter).

Furthermore, in the TD direction, in the distance a₁ between thereinforcing core materials adjacent to each other of 1056 μm, the numbern of elution holes provided between the adjacent reinforcing corematerials was 2 and the distance c₁ of the adjacent elution holes was203 μm. According to calculation, the distance c₁ was expressed by0.58a₁/(n+1).

Moreover, in the MD direction, in the distance a₂ between thereinforcing core materials adjacent to each other of 1192 μm, the numbern of elution holes provided between the adjacent reinforcing corematerials was 2 and the distance c₂ of the adjacent elution holes was528 μm. According to calculation, the distance c₂ was expressed by1.33a₂/(n+1).

In the MD direction, in the distance a₁ between the reinforcing corematerials adjacent to each other of 998 μm, the number n of elutionholes provided between the adjacent reinforcing core materials was 2 andthe distance c₁ of the adjacent elution holes was 296 μm. According tocalculation, the distance c₁ was expressed by 0.89a₁/(n+1).

The physical properties of the obtained cation exchange membrane areshown in Table 1. In Table 1, the interval units between reinforcingcore materials, which were alternately arranged in adjacent to eachother in the TD direction of the cation exchange membrane in Example 1were respectively designated as reinforcing core material interval T1and reinforcing core material interval T2. Furthermore, In the MDdirection, repeated constitutional units were designated as reinforcingcore material interval M1 and reinforcing core material interval M2.Also as to the following Examples and Comparative Examples, descriptionwas made in the table similarly. As shown in Table 1, it was confirmedthat the cation exchange membrane had a high tensile elongationretaining rate in either one of MD folding and TD folding.

Example 2

A cation exchange membrane was prepared by using the same materials asin Example 1 except that a yarn (PVA yarn) of 15-filament polyvinylalcohol (PVA) of 28 deniers twisted 200 times/m was used as a dummyyarn.

In the obtained cation exchange membrane, in the TD direction, thedistance a₂ between the reinforcing core materials adjacent to eachother was 1005 μm, the number n of elution holes provided between theadjacent reinforcing core materials was 2 and the distance c₂ of theadjacent elution holes was 373 μm. According to calculation, thedistance c₂ was expressed by 1.11a₂/(n+1) (see FIG. 8, the samehereinafter).

Furthermore, in the TD direction, in the distance a₁ between thereinforcing core materials adjacent to each other of 1091 μm, the numbern of elution holes provided between the adjacent reinforcing corematerials was 2 and the distance c₁ of the adjacent elution holes was252 μm. According to calculation, the distance c₁ was expressed by0.69a₁/(n+1).

Moreover, in the MD direction, in the distance a₂ between thereinforcing core materials adjacent to each other of 1199 μm, the numbern of elution holes provided between the adjacent reinforcing corematerials was 2 and the distance c₂ of the adjacent elution holes was500 μm. According to calculation, the distance c₂ was expressed by1.25a₂/(n+1).

In the MD direction, in the distance a₁ between the reinforcing corematerials adjacent to each other of 999 μm, the number n of elutionholes provided between the adjacent reinforcing core materials was 2 andthe distance c₁ between the adjacent elution holes was 266 μm. Accordingto calculation, the distance c₁ was expressed by 0.80a₁/(n+1).

The physical properties of the obtained cation exchange membrane areshown in Table 1. As shown in Table 1, it was confirmed that the cationexchange membrane had a high tensile elongation retaining rate in eitherone of MD folding and TD folding.

Example 3

First, PTFE yarns were arranged at a rate of 24 yarns/inch atapproximately equal intervals. MD yarns were prepared by use of acontinuous 3-dent reed as follows. A bundle of 2 yarns consisting ofPTFE yarn and PET yarn was passed through a first reed; a bundle of 2yarns consisting of PET yarn and PTFE yarn was passed through a secondreed; and a bundle of 2 yarns consisting of PET yarn and PET yarn waspassed through a third reed. Weaving of the bundles of yarns in thiscombination was repeated in this order to obtain a plain weave. As to TDyarns, PTFE yarn, PVA yarn, PVA yarn, PET yarn, PET yarn, PVA yarn andPVA yarn were arranged in this order repeatedly and at approximatelyequal intervals to obtain a plain weave. In this manner, a woven fabric(reinforcing material) was obtained. Subsequently, the obtainedreinforcing material was subjected to contact bonding performed by aroll heated to 125° C. Thereafter, the reinforcing material was soakedin a 0.1 N aqueous sodium hydroxide solution to dissolve a dummy yarn(PVA yarn) alone and remove it from the reinforcing material. Thethickness of the reinforcing material from which the dummy yarn wasremoved was 85 μm. A cation exchange membrane was prepared in the samemanner as in Example 1 except the above.

In the obtained cation exchange membrane, in the TD direction, thedistance a₁ between the reinforcing core materials adjacent to eachother was 1119 μm, the number n of elution holes provided between theadjacent reinforcing core materials was 2 and the distance c₁ of theadjacent elution holes was 255 μm. According to calculation, thedistance c₁ was expressed by 0.68a₁/(n+1) (see FIG. 8, the samehereinafter).

Furthermore, in the MD direction, the distance a₂ between thereinforcing core materials adjacent to each other was 1229 μm, thenumber n of elution holes provided between the adjacent reinforcing corematerials was 2 and the distance c₂ of the adjacent elution holes was569 μm. According to calculation, the distance c₂ was expressed by1.39a₂/(n+1).

Moreover, in the MD direction, the distance a₁ between the reinforcingcore materials adjacent to each other was 985 μm, the number n ofelution holes provided between the adjacent reinforcing core materialswas 2 and the distance c₁ of the adjacent elution holes was 323 μm.According to calculation, the distance c₁ was expressed by 0.98a₁/(n+1).

The physical properties of the obtained cation exchange membrane areshown in Table 1. As shown in Table 1, it was confirmed that the cationexchange membrane had a high tensile elongation retaining rate in eitherone of MD folding and TD folding.

Example 4

First, PTFE yarns were arranged at a rate of 24 yarns/inch atapproximately equal intervals. MD yarns were prepared by use of acontinuous 3-dent reed as follows. A bundle of 2 yarns consisting ofPTFE yarn and PET yarn was passed through a first reed; a bundle of 2yarns consisting of PET yarn and PTFE yarn was passed through a secondreed and a bundle of 2 yarns consisting of PET yarn and PET yarn waspassed through a third reed. Weaving of the bundles of yarns in thiscombination was repeated in this order to obtain a plain weave. As to TDyarns, PTFE yarn, PET yarn and PET yarn were arranged at approximatelyequal interval sequentially in this order repeatedly to obtain a plainweave. In this manner, a woven fabric (reinforcing material) wasobtained. Subsequently, the obtained reinforcing material was subjectedto contact bonding performed by a roll heated to 125° C. Thereafter, theobtained reinforcing material was soaked in a 0.1 N aqueous sodiumhydroxide solution to dissolve a dummy yarn (PVA yarn) alone and removeit from the reinforcing material. The thickness of the reinforcingmaterial from which the dummy yarn was removed was 76 μm. A cationexchange membrane was prepared in the same manner as in Example 1 exceptthe above.

In the obtained cation exchange membrane, in the TD direction, thedistance a₁ between the reinforcing core materials adjacent to eachother was 1092 μm, the number n of elution holes provided between theadjacent reinforcing core materials was 2 and the distance c₁ betweenthe adjacent elution holes was 364 μm. According to calculation, thedistance c₁ was expressed by 1.00a₁/(n+1).

In the MD direction, the distance a₂ between the reinforcing corematerials adjacent to each other was 1178 μm, the number n of elutionholes provided between the adjacent reinforcing core materials was 2 andthe distance c₂ of the adjacent elution holes was 509 μm. According tocalculation, the distance c₂ was expressed by 1.30a₂/(n+1) (see FIG. 8,the same hereinafter).

In the MD direction, the distance a₁ between the reinforcing corematerials adjacent to each other was 930 μm, the number n of elutionholes provided between the adjacent reinforcing core materials was 2 andthe distance c₁ between the adjacent elution holes was 253 μm. Accordingto calculation, the distance c₁ was expressed by 0.82a₁/(n−1).

The physical properties of the obtained cation exchange membrane areshown in Table 1. As shown in Table 1, it was confirmed that the cationexchange membrane had a high tensile elongation retaining rate in TDfolding.

Comparative Example 1

A cation exchange membrane was produced having elution holes formed atequal intervals both in the MD direction and in the TD direction. As areinforcing core material, a monofilament made bypolytetrafluoroethylene (PTFE) of 90 deniers (PTFE yarn) was used. As asacrifice yarn, a yarn formed of 6-filament polyethylene terephthalate(PET) of 40 deniers and twisted at a rate of 200 twists/m (PET yarn) wasused.

First, PTFE yarns were arranged at a rate of 24 yarns/inch at equalintervals. As to MD yarns, PTFE yarn, PET yarn and PET yarn . . . werearranged in this order repeatedly to obtain a plain weave. Also as to TDyarns, PTFE yarn, PET yarn and PET yarn . . . were arranged repeatedlyto obtain a plain weave. In this manner, a woven fabric (reinforcingmaterial) was obtained. Subsequently, the obtained reinforcing materialwas subjected to contact bonding performed by a roll heated andcontrolled so as to have a thickness of 86 μm. The cation exchangemembrane was obtained in the same manner as in Example 1 except theabove.

In the cation exchange membrane, in the TD direction, the distance a₁between the reinforcing core materials adjacent to each other was 1058μm, the number n of elution holes provided between the adjacentreinforcing core materials was 2 and the distance c₁ of the adjacentelution holes was 353 μm. According to calculation, the distance c₁ wasexpressed by 1.00a₁/(n+1) (see FIG. 8, the same hereinafter).

In the MD direction, the distance a₁ between the reinforcing corematerials adjacent to each other was 1058 μm, the number n of elutionholes provided between the adjacent reinforcing core materials was 2 andthe distance c₁ between the adjacent elution holes was 353 μm. Accordingto calculation, the distance c₁ was expressed by 1.00a₁/(n+1).

The physical properties of the cation exchange membranes of Examples 1to 4 and Comparative Example 1 are shown in Table 1. Note that, thesymbol “-” in the table indicates that no corresponding substance ispresent in Examples and Comparative Examples. As shown in Table 1, itwas confirmed that the cation exchange membrane of each Example had ahigh tensile elongation retaining rate in either one of MD folding andTD folding.

TABLE 1 Comparative Example 1 Example 2 Example 3 Example 4 Example 1Reinforcing Material PTFE PTFE PTFE PTFE PTFE yarn Denier 90 90 90 90 90Filament mono mono mono mono mono Sacrifice yarn Material PET PET PETPET PET Denier 30 30 40 40 40 Filament 6 6 6 6 6 Twisting 200 200 200200 200 times Dummy yarn Material PVA PVA PVA — — Denier 36 28 36 — —Filament 15 15 l5 — — Twisting 200 200 200 — — times Thickness ofreinforcing material 81 84 85 76 86 (μm) n 2 2 2 2 2 Yarn T1 a₁ 10561091 1119 1092 1058 interval b₁ 426.5 419.5 432 364 352.5 (TD direction)c₁ 203 252 255 364 353 b₁/(a₁/(n + 1)) 1.21 1.15 1.16 1.00 1.00c₁/(a₁/(n + 1)) 0.58 0.69 0.68 1.00 1.00 T2 a₂ 1112 1005 — — — b₂ 340316 — — — c₂ 432 373 — — — c₂/(a₂/(n + 1)) 1.17 1.11 — — — Yarn M1 a₁998 999 985 930 1058 interval b₁ 351 366.5 331 338.5 352.5 (MDdirection) c₁ 296 266 323 253 353 b₁/(a₁/(n + 1)) 1.06 1.10 1.01 1.091.00 c₁/(a₁/(n + 1)) 0.89 0.80 0.98 0.82 1.00 M2 a₂ 1192 1199 1229 1178— b₂ 332 349.5 330 334.5 — c₂ 528 500 569 509 — c₂/(a₂/(n + 1)) 1.331.25 1.39 1.30 — Folding resistance MD 63 51 58 42 41 (%) (TensileFolding elongation TD 72 76 70 82 41 retention rate (%)) Folding

Example 5

First, PTFE yarns were arranged at a rate of 24 yarns/inch atapproximately equal intervals. MD yarns were prepared by use of acontinuous 3-dent reed as follows. A bundle of 2 yarns consisting ofPTFE yarn and PET yarn was passed through a first reed; a bundle of 2yarns consisting of PET yarn and PTFE yarn was passed through a secondreed; and a bundle of 2 yarns consisting of PET yarn and PET yarn waspassed through a third reed. Weaving of the bundles of yarns in thiscombination was repeated in this order to obtain a plain weave. As to TDyarns, PTFE yarn, PET yarn, PVA yarn, PVA yarn, PVA yarn, PVA yarn andPET yarn were arranged in this order repeatedly and at approximatelyequal intervals to obtain a plain weave. In this manner, a woven fabric(reinforcing material) was obtained. Subsequently, the obtainedreinforcing material was subjected to contact bonding performed by aroll heated to 125° C. Thereafter, the reinforcing material was soakedin a 0.1 N aqueous sodium hydroxide solution to dissolve a dummy yarn(PVA yarn) alone and remove it from the reinforcing material. Thethickness of the reinforcing material from which the dummy yarn wasremoved was 85 μm. A cation exchange membrane was prepared in the samemanner as in Example 1 except the above.

In the cation exchange membrane, in the TD direction, the distance a₁between the reinforcing core materials adjacent to each other was 1040μm, the number n of elution holes provided between the adjacentreinforcing core materials was 2 and the distance c₁ between theadjacent elution holes was 448 μm. Accordingly, the distance c₁ wasexpressed by 1.29a₁/(n+1) (see FIG. 8, the same hereinafter). In the TDdirection of the cation exchange membrane of Example 5, the only theinterval between reinforcing core materials having the aforementioneda1, b1, c1 values was arranged.

In the MD direction, the distance a₂ between the reinforcing corematerials adjacent to each other was 1151 μm, the number n of elutionholes provided between the adjacent reinforcing core materials was 2 andthe distance c₂ between the adjacent elution holes was 478 μm.Accordingly, the distance c₂ was expressed by 1.25a₂/(n+1). In the MDdirection, the distance a₁ between the reinforcing core materialsadjacent to each other was 944 μm, the number n of elution holesprovided between the adjacent reinforcing core materials was 2 and thedistance c₁ of the adjacent elution holes was 269 μm. Accordingly, thedistance c₁ was expressed by 0.85a₁/(n+1).

As evaluation of mechanical strength, the cation exchange membrane wasfolded by applying weight of 400 g/cm² so as to allow the surface of thecarboxylic acid layer side (see FIG. 1, the carboxylic acid layer 144,and “polymer A layer” described above) to face inside and the presenceor absence of e.g., pinhole formation was observed. In the obtainedcation exchange membrane of Example 5, formation of a pinhole by foldingwas not confirmed.

In Examples 1 to 5 and Comparative Example 1, electrolysis was performedby use of the obtained cation exchange membrane and electrolysis voltagewas measured. The results are shown in Table 2.

TABLE 2 Comparative Example 1 Example 2 Example 3 Example 4 Example 5Example 1 Electrolysis 3.22 3.26 3.31 3.37 3.30 3.45 voltage (V)

As shown in Table 2, when electrolysis was performed by using the cationexchange membrane of each Example, it was confirmed that electrolysisvoltage was reduced compared to Comparative Example 1. Furthermore, whenan electrolysis operation was performed for 7 days, electrolysis couldbe stably performed.

From the above, it was demonstrated that the cation exchange membrane ofeach Example was excellent in mechanical strength against folding, etc.As a result, it was demonstrated that stable electrolytic performancecan be delivered for a long time. It was further demonstrated that, inthe cation exchange membrane of each Example, electrolysis voltage canbe reduced compared to the cation exchange membrane where elution holeswere formed at equal intervals, and excellent electrolytic performancecan be delivered.

Example 6

First, PTFE yarns were arranged at a rate of 24 yarns/inch atapproximately equal intervals. MD yarns were prepared by use of acontinuous 5-dent reed as follows. A bundle of 2 yarns consisting ofPTFE yarn and PET yarn was passed through a first reed; a bundle of 2yarns consisting of PET yarn and PET yarn was passed through a secondreed; a bundle of 2 yarns consisting of PET yarn and PTFE yarn waspassed through a third reed; a bundle of 2 yarns consisting of PET yarnand PET yarn was passed through a fourth reed; and a bundle of 2 yarnsconsisting of PET yarn and PET yarn was passed through a fifth reed.Weaving of the bundles of yarns in this combination was repeated in thisorder to obtain a plain weave. As to TD yarns, PTFE yarn, PET yarn, PETyarn, PVA yarn, PVA yarn, PET yarn and PET yarn were arranged in thisorder repeatedly and at approximately equal intervals to obtain a plainweave. In this manner, a woven fabric (reinforcing material) wasobtained. Subsequently, the obtained reinforcing material was subjectedto contact bonding performed by a roll heated to 125° C. Thereafter, theobtained reinforcing material was soaked in a 0.1 N aqueous sodiumhydroxide solution to dissolve a dummy yarn (PVA yarn) alone and removeit from the reinforcing material. The thickness of the reinforcingmaterial from which the dummy yarn was removed was 93 μm. The cationexchange membrane 8 shown in FIG. 9 was prepared in the same manner asin Example 1 except the above. The cation exchange membrane 8 had themembrane body (not shown) and two or more reinforcing core materials 80arranged approximately in parallel within the membrane body. Themembrane body had a structure where 4 elution holes were formed betweenthe reinforcing core materials 80 adjacent to each other. Morespecifically, four elution holes 821, 822, 823, 824 were formed atrespective intervals of a, b, c₁, c₂ between the reinforcing corematerials 80.

In the obtained cation exchange membrane, in the TD direction, thedistance a between the reinforcing core materials adjacent to each otherwas 1521 μm, the number n of elution holes provided between the adjacentreinforcing core materials was 4, the distance b of the reinforcing corematerial and the adjacent elution hole was 268 μm and the distance c₁between the elution hole and the adjacent elution hole was 265 μm. Thedistance c₂ between the two elution holes at the center was 443 μm (seeFIG. 9).

Furthermore, in the MD direction, elution holes were formed at equalintervals between the reinforcing core materials.

The physical properties of the obtained cation exchange membrane areshown in Table 3. As is shown in Table 3, it was confirmed that thecation exchange membrane had a high tensile elongation retaining rate inMD folding compared to Comparative Example 2. Furthermore, it wasconfirmed that the electrolysis voltage thereof was lower than that ofComparative Example 2.

Example 7

First, PTFE yarns were arranged at a rate of 24 yarns/inch atapproximately equal intervals. MD yarns were prepared by use of acontinuous 5-dent reed as follows. A bundle of 2 yarns consisting ofPTFE yarn and PET yarn was passed through a first reed; a bundle of 2yarns consisting of PET yarn and PET yarn was passed through a secondreed; a bundle of 2 yarns consisting of PET yarn and PTFE yarn waspassed through a third reed; a bundle of 2 yarns consisting of PET yarnand PET yarn was passed through a fourth reed; and a bundle of 2 yarnsconsisting of PET yarn and PET yarn was passed through a fifth reed.Weaving of the bundles of yarns in this combination was repeated in thisorder to obtain a plain weave. As to TD yarns, PTFE yarn, PET yarn, PVAyarn, PVA yarn, PET yarn, PET yarn, PVA yarn, PVA yarn and PET yarn werearranged in this order repeatedly and at approximately equal intervalsto obtain a plain weave. In this manner, a woven fabric (reinforcingmaterial) was obtained. Subsequently, the obtained reinforcing materialwas subjected to contact bonding performed by a roll heated to 125° C.Thereafter, the reinforcing material was soaked in a 0.1 N aqueoussodium hydroxide solution to dissolve a dummy yarn alone and remove itfrom the reinforcing material. The thickness of the reinforcing materialfrom which the dummy yarn was removed was 93 μm. A cation exchangemembrane was prepared in the same manner as in Example 6 except theabove.

In the cation exchange membrane, in the TD direction, the distance abetween the reinforcing core materials adjacent to each other was 1523μm, the number n of elution holes provided between the adjacentreinforcing core materials was 4, the distance b of the reinforcing corematerial and the adjacent elution hole was 264 μm and the distance c₁ ofthe elution hole and the adjacent elution hole was 361 μm. The distancec₂ between the two elution holes at the center was 245 μm (see FIG. 9).

Furthermore, in the MD direction, elution holes were formed at equalintervals between the reinforcing core materials.

Comparative Example 2

A cation exchange membrane was produced having elution holes formed atequal intervals both in the MD direction and in the TD direction. As areinforcing core material, a monofilament polytetrafluoroethylene (PTFE)of 90 deniers (PTFE yarn) was used. As a sacrifice yarn, 6-filamentpolyethylene terephthalate (PET) of 40 deniers twisted at a rate of 200twists/m (PET yarn) was used.

First, PTFE yarns were arranged at a rate of 16 yarns/inch at equalintervals. As to MD yarn, PTFE yarn, PET yarn, PET yarn, PET yarn andPET yarn were arranged in this order repeatedly to obtain a plain weave.Also as to TD yarn, PTFE yarn, PET yarn, PET yarn, PET yarn and PET yarnwere arranged repeatedly to obtain a plain weave thereby producing awoven fabric (reinforcing material). Subsequently, the obtainedreinforcing material was subjected to contact bonding performed by aroll heated to 125° C. and controlled so as to have a thickness of 85μm. A cation exchange membrane was obtained in the same manner as inExample 6 except the above.

In the cation exchange membrane, in the TD direction, the distance abetween the reinforcing core materials adjacent to each other was 1517μm, the number n of elution holes provided between the adjacentreinforcing core materials was 4, the distance b between the reinforcingcore material and the adjacent elution hole was 303 μm and the distancec₁ between the elution hole and the adjacent elution hole was 303 μm.The distance c₂ between the two elution holes at the center was 303 μm(see FIG. 9).

Furthermore, in the MD direction, elution holes were formed at equalintervals between the reinforcing core materials.

The physical properties of the cation exchange membranes of Example 6, 7and Comparative Example 2 are shown in Table 3. As shown in Table 3, inExample 6, 7, it was confirmed that the cation exchange membrane had ahigh tensile elongation retaining rate also after folding. Furthermore,as is shown in Table 3, when electrolysis was performed by using thecation exchange membrane of each Example, it was confirmed thatelectrolysis voltage was reduced compared to Comparative Example 2.Furthermore, when an electrolysis operation was performed for 7 days,electrolysis can be stably performed.

TABLE 3 Comparative Example 6 Example 7 Example 2 Reinforcing MaterialPTFE PTFE PTFE yarn Denier 90 90 90 Filament mono mono mono Sacrificeyarn Material PET PET PET Denier 30 40 40 Filament 6 6 6 Twisting times200 200 200 Dummy yarn Material PVA PVA PVA Denier 36 36 36 Filament 1515 15 Twisting times 200 200 200 Thickness of reinforcing 93 93 85material (μm) n 4 4 4 Yarn TD a 1521 1523 1517 interval direc- b 268 264303 tion c₁ 265 361 303 c₂ 443 245 303 c₁/(a/(n + 1)) 0.9 1.2 1.0c₂/(a/(n + 1)) 1.5 0.8 1.0 Folding MD 44 44 28 resistance (%) Folding(Tensile elongation retention rate (%)) Electrolysis voltage (V) 3.263.26 3.31

From the above, it was demonstrated that the cation exchange membrane ofeach Example was excellent in mechanical strength against folding, etc.As a result, it was demonstrated that electrolytic performance could bestably delivered for a long time. Furthermore, it was demonstrated thatin the case where the cation exchange membrane of each Example was used,electrolysis voltage could be reduced compared to the case where thecation exchange membrane having the reinforcing core materials whereelution holes were formed at equal intervals, and that excellentelectrolytic performance could be delivered.

Example 8

First, PTFE yarns were arranged at a rate of 24 yarns/inch atapproximately equal intervals. MD yarns were prepared by use of acontinuous 5-dent reed as follows. A bundle of 2 yarns consisting ofPTFE yarn and PET yarn was passed through a first reed; a bundle of 2yarns consisting of PET yarn and PET yarn was passed through a secondreed; a bundle of 2 yarns consisting of PET yarn and PTFE yarn waspassed through a third reed; a bundle of 2 yarns consisting of PET yarnand PET yarn was passed through a fourth reed; and a bundle of 2 yarnsconsisting of PET yarn and PET yarn was passed through a fifth reed.Weaving of the bundles of yarns in this combination was repeated in thisorder to obtain a plain weave. As to TD yarns, PTFE yarn, PVA yarn, PVAyarn, PET yarn, PET yarn, PET yarn, PET yarn, PVA yarn and PVA yarn werearranged in this order repeatedly and at approximately equal intervalsto obtain a plain weave. In this manner, a woven fabric (reinforcingmaterial) was obtained. Subsequently, the obtained reinforcing materialwas subjected to contact bonding performed by a roll heated to 125° C.Thereafter, the reinforcing material was soaked in a 0.1 N aqueoussodium hydroxide solution to dissolve a dummy yarn (PVA yarn) alone andremove it from the reinforcing material. The thickness of thereinforcing material from which the dummy yarn was removed was 95 μm. Acation exchange membrane was prepared in the same manner as in Example 1except the above.

In the obtained cation exchange membrane, in the TD direction, thedistance a between the reinforcing core materials adjacent to each otherwas 1559 μm, the number n of elution holes provided between the adjacentreinforcing core materials was 4, the distance b of the reinforcing corematerial and the adjacent elution hole was 463 μm and the distance c₁ ofthe elution hole and the adjacent elution hole was 206 μm. The distancec₂ between the two elution holes at the center was 180 μm (see FIG. 9).

Example 9

First, PTFE yarns were arranged at a rate of 24 yarns/inch atapproximately equal intervals. MD yarns were prepared by use of acontinuous 5-dent reed as follows. A bundle of 2 yarns consisting ofPTFE yarn and PET yarn was passed through a first reed; a bundle of 2yarns consisting of PET yarn and PET yarn was passed through a secondreed; a bundle of 2 yarns consisting of PET yarn and PTFE yarn waspassed through a third reed; a bundle of 2 yarns consisting of PET yarnand PET yarn was passed through a fourth reed; and a bundle of 2 yarnsconsisting of PET yarn and PET yarn was passed through a fifth reed.Weaving of the bundles of yarns in this combination was repeated in thisorder to obtain a plain weave. As to TD yarns, PTFE yarn, PET yarn, PETyarn, PVA yarn, PVA yarn, PET yarn, PET yarn, PTFE yarn, PET yarn, PVAyarn, PVA yarn, PET yarn, PET yarn, PVA yarn, PVA yarn and PET yarn werearranged in this order repeatedly and at approximately equal intervalsto obtain a plain weave. In this manner, a woven fabric (reinforcingmaterial) was obtained. Subsequently, the obtained reinforcing materialwas subjected to contact bonding performed by a roll heated to 125° C.Thereafter, the reinforcing material was soaked in a 0.1 N aqueoussodium hydroxide solution to dissolve a dummy yarn (PVA yarn) alone andremove it from the reinforcing material. The thickness of thereinforcing material from which the dummy yarn was removed was 92 μm.The cation exchange membrane was prepared in the same manner as inExample 1 except the above.

In the obtained cation exchange membrane, in the TD direction, thedistance a between the reinforcing core materials adjacent to each otherwas 1743 μm, the number n of elution holes provided between the adjacentreinforcing core materials was 4, the distance b between the reinforcingcore material and the adjacent elution hole was 201 μm and the distancec₁ between the elution hole and the adjacent elution hole was 470 μm.The distance c₂ between the two elution holes at the center was 255 μm(see FIG. 9).

Furthermore, in the case where the distance a between the reinforcingcore materials adjacent to each other was 1387 μm, the number n ofelution holes provided between the adjacent reinforcing core materialswas 4 and the distance b between the reinforcing core material and theadjacent elution hole was 228 μm and the distance c₁ between the elutionhole and the adjacent elution hole was 462 μm. The distance c₂ betweenthe two elution holes at the center was 218 μm (see FIG. 9).

The physical properties of the cation exchange membranes of Examples 8and 9 are shown in Table 4. Note that, the symbol “-” in the tableindicates that no corresponding substance was present in the Examplesand Comparative Examples.

TABLE 4 Example 8 Example 9 Reinforcing Material PTFE PTFE yarn Denier90 90 Filament mono mono Sacrifice Material PET PET yarn Denier 40 40Filament 6 6 Twisting times 200 200 Dummy yarn Material PVA PVA Denier36 36 Filament 15 15 Twisting times 200 200 Thickness of reinforcingmaterial 95 92 (μm) N 4 4 Yarn interval T1 A 1559 1743 (TD direction) B463 201 c₁ 206 470 c₂ 180 255 c₁/(a/(n + 1)) 0.66 1.35 c₂/(a/(n + 1))0.58 0.73 T2 A — 1387 B — 228 c₁ — 462 c₂ — 218 c₁/(a/(n + 1)) — 1.67c₂/(a/(n + 1)) — 0.79

As evaluation of mechanical strength, the cation exchange membrane wasfolded by applying weight of 400 g/cm² so as to allow the surface of thecarboxylic acid layer side (see FIG. 1, the carboxylic acid layer 144,and “polymer A layer” described above) to face inside and the presenceor absence of e.g., pinhole formation was observed. In the obtainedcation exchange membrane of Examples 8 and 9, formation of a pinhole byfolding was not confirmed. In addition, it was discovered that stableelectrolytic performance can be delivered for a long time.

This application is based on Japanese Patent Application No. 2009-245869which was filed with Japan Patent Office on Oct. 26, 2009, which ishereby incorporated by reference herein.

INDUSTRIAL APPLICABILITY

The cation exchange membrane of the present invention can be suitablyused as the cation exchange membrane for alkali chloride electrolysis,etc.

REFERENCE SIGNS LIST

-   1, 2, 3, 4, 5 . . . Cation exchange membrane,-   6 . . . Reinforcing material,-   10, 20 x, 20 y, 301, 302, 303, 401, 402, 403, 501 x, 501 y, 502 x,    502 y, 503 x, 503 y, 60 . . . Reinforcing core material,-   12, 12 a, 12 b, 22 x, 22 y, 321, 322, 323, 324, 325, 326, 421, 422,    423, 424, 521 x, 521 y, 522 x, 522 y, 523 x, 523 y, 524 x, 524 y . .    . Elution holes,-   14 . . . Membrane body,-   62 . . . Sacrifice yarn,-   66 . . . Dummy yarn,-   142 . . . Sulfonic acid layer,-   144 . . . Carboxylic acid layer,-   146, 148 . . . Coating layer,-   A . . . Electrolysis vessel,-   A1 . . . Anode,-   A2 . . . Cathode,-   α . . . Anode side,-   β . . . Cathode side,-   X . . . MD direction,-   Y . . . TD direction

What is claimed is:
 1. A method for producing a cation exchangemembrane, comprising the steps of: weaving two or more reinforcing corematerials, a sacrifice yarn soluble in an acid or an alkali, and a dummyyarn soluble in a predetermined solvent in which the reinforcing corematerials and the sacrifice yarn are insoluble, to obtain a reinforcingmaterial having the sacrifice yarn and the dummy yarn arranged betweenthe reinforcing core materials adjacent to each other; soaking thereinforcing material in the predetermined solvent to remove the dummyyarn from the reinforcing material; stacking the reinforcing materialfrom which the dummy yarn is removed and a fluorine-based polymer havingan ion-exchange group or an ion-exchange group precursor which can beconverted into the ion-exchange group by hydrolysis, to form a membranebody having the reinforcing material; and soaking the sacrifice yarn inan acid or an alkali to remove the sacrifice yarn from the membranebody, thereby forming an elution hole in the membrane body.